As an offshoot of the Arianist question, which major heresy (or whatever term you prefer) had the least reasonable philosophical and theological grounding?
If we're talking
major heretical groups, I'd say gnosticism in general. It was a fundamentally world-denying movement - a fetishisation of death and denial of life. And they had some truly wacky christologies too; people think Nestorianism is bad enough for making Jesus into two people, but some of the gnostics thought there were five of him.
I think Averroism was pretty extraordinary, although it's questionable to what extent anyone actually was an Averroist, even Siger of Brabant, who's normally cited as its main exponent. It seems to me just bizarre to suggest that there is only a single human mind, and we all share it.
What about the verse when it says "There was no death until Adam sinned."
I don't know what verse you're referring to or what relevance you think it has. If you want to discuss things like this seriously it's not good enough just to make vague reference to some half-remembered text without citation; you have to say exactly why you're citing it.
More generally, though, let me try to make this issue clearer. It really doesn't matter what verses you pick and choose from the Bible to try to support something like young earth creationism. The whole process of doing this - of picking and choosing biblical verses to support such a crazy view - is totally lopsided from the start. This is not what Christianity is supposed to be about. It is not supposed to be about making the Bible into a sole and infallible source of knowledge of every kind, even scientific knowledge, even where that goes totally against what rational investigation of the world shows us. Why? Because Christianity is supposed to be founded upon reason. Haven't you ever read the opening verses of John's Gospel? Remember that stuff about the
Logos and how the world was made through him?
Logos means
reason. It is saying that Christ is the divine reason, and that God made the world in accordance with the rational Christ. The world is therefore rational because it was created through the divine reason.
Furthermore, if you read on, you will find that the
Logos is the divine light that illuminates human beings. In other words, we are rational too, because we have some sharing in the divine reason, namely Christ.
These ideas were absolutely fundamental to the subsequent development of Christian theology. You find them repeated and expanded in Justin Martyr, for example, the first patristic theologian. You find them in Clement of Alexandria, who makes the
Logos into the
Pedagogos, that is, the teacher of humanity. And in a different form, you find them in the development of doctrines such as the incarnation and the Trinity, which emerged through a process of rational meditation (and bickering) upon the doctrines delivered by the first apostles.
Most of all, you find these ideas in the great synthesis of Christian and classical learning which appeared in the fourth and fifth centuries, when people like Basil of Caesarea, Gregory of Nyssa, Ambrose of Milan, Augustine of Hippo, and countless of other less stellar names set out their understanding of Christianity in terms drawn from the secular learning of the time. Why? Because they understood that Christ is the Logos, that God is rational, and that the divine religion is rational. That means it can use the best bits of human reason - there is no fundamental contradiction between what faith reveals and what reason shows, although the latter is certainly fallible and may need to be corrected by the former.
This was the basis for the whole of medieval philosophy and theology, including the system of Thomas Aquinas. The medievals made very strong and clear distinctions between different branches of learning - or "sciences" as they called - but they firmly believed that all of the sciences were actually studying the same thing, though in different ways - namely reality, as created and revealed by God.
Now the whole tendency of Protestant fundamentalism, and young earth creationism above all, is totally opposed to this historic nature of Christianity. It denies that Christianity is rational at all, because it expects people to ignore what reason tells them and believe something irrational. Worse, it denies that the world is rational at all, because it asserts that everything about the world is misleading: that all of the vast body of evidence for modern science is actually wrong and even actively mendacious. It pits not simply religion against science but faith against the world. Not just against reason, but against the world itself. It denies faith in God as rational and in Christ as the reason of God through whom the world is made. Ultimately I'd say it's actually rather like gnosticism, which also denied the importance and goodness of the world, though in a very different way.
I don't care if there is some verse in the Bible that supports "young earth creationism", or indeed lots of verses, because true Christianity isn't just about slavishly following whatever the Bible says
even when it is blatantly wrong, and it never has been. Did Paul think that the creation account in Genesis was literally true? Yes, probably, but then why shouldn't he have? He didn't have any reason to think otherwise. We are not in that position. We do have very good reasons to think otherwise. Why, then, should we share Paul's view on this matter? Paul no doubt also thought that the sun revolves around the earth, having no good reason to think otherwise. We don't share that view of his. If he'd happened to have mentioned it in passing in one of his letters, would Christians be bound to believe the same thing for ever more even though it's completely absurd in the light of modern astronomical knowledge? Of course not.
Authentic Christianity, in my opinion, does not put any source of faith on a pedestal so high that it is untouchable and cannot be contradicted by another source. That is because authentic Christianity recognises the value of many different sources of faith - the Bible, yes, but also tradition, church teaching, personal experience, and reason. Protestant fundamentalism is a diminished, weak sort of Christianity, a feeble stripped-down version that would rob us of all those other things and replace them with the Bible alone. That's not even possible, as LightSpectra so frequently reminds us, and even if it were possible, it would not be desirable.
That is why modern theologians don't waste any more time on "young earth creationism" than modern scientists do. It is why the absolute worthless drivel spouted by "young earth creationists" is not worthy of our attention even from a purely theological viewpoint, never mind a scientific one.
I do sometimes think that Protestant fundamentalists would be much happier being Muslims. The fundamentalist view of the Bible developed quite independently of the Muslim view of the Koran, as far as I know, but I do wonder if its subsequent defence might have been influenced by it to at least some degree. You see, Muslim theology really is predicated upon the all-sufficiency and inerrancy of the Koran as containing God's direct communication to human beings - hence the importance of knowing Arabic for Muslims, since they take this idea quite seriously and therefore suppose that the language of the Koran is significant. The traditional Muslim view is that the Koran tells us everything we need to know, and the role of reason is to understand, interpret, explain, and defend what the Koran teaches. Protestant fundamentalists would do exactly the same thing, except with the Bible instead of the Koran. But that's a perversion of historical Christianity.
I dont know that divinely inspired commentary on our existence requires 100% accuracy. The Bible is full of examples of "God" making mistakes or revealing ignorance, and thats without getting into their earlier pagan gods.
Right, so why's it so important to defend the idea that the Genesis account is right at all? Why is it so significant that they got some bits roughly right, if its being wrong is consistent even with its being divine revelation?
somebody way back when knew the world was covered with water before some cataclysm (a celestial battle or act of creation) produced "dry land" and life. They were right...
Whether they were right or not, they didn't "know" it. They guessed. At most, they believed it. Some of the things they believed turned out, by total coincidence, to be true. Most of the things they believed turned out to be false. What does that tell us? Nothing whatsoever.
The Sumerians were the first to write this stuff down and they had a creation of man myth claiming the gods bound their image onto a creature roaming some lands to the south where Enki (water and serpent deity) reigned. They messed with some critter already here to make slave labor (there was no Adam to till the land). There is no conflict with their version and evolution. But it should show up as a "jump" in our evolution, and it does.
Are you talking about the story of Enkidu in the Epic of Gilgamesh? Because the story doesn't suggest that Enkidu was a non-human animal, merely that he was an uncivilised human being; the story is about the rise of civilisation, not the evolution of humanity. And of course, he wasn't civilised in order to till the land, but to distract Gilgamesh from all his endless wrestling, which was really annoying everyone.
Another one, is Solomon the author of Ecclesiastes?
No.
On a related note -- I have some vague recollection of Augustine making some point about there being multiple ages through history, including an indeterminate period of time before Adam. Is my memory just butchering Augustine's bit about the six ages of men? Are you aware of any of his writings along that topic? (What about other early Christian writers? I'm pretty sure it was Augustine, although I suppose I could be messing that up as well)
I'm afraid I don't know; in fact I can't think of any patristic author saying that there was an indeterminate amount of time before Adam, although that doesn't mean that none did. The closest I can think of off-hand is Origen, who believed that there were worlds before ours, and there will be worlds after ours, and that Adam never existed anyway but is an allegory; but that's not quite what you're thinking of.
Seriously, the new theory is comets (< 10%) and asteroids brought us the water. Of course that begs the question: if the increasing antiquity of our oceans shortens the time frame for comets to bring us the water, why would asteroids be the answer? So why are these theorists trying to bring us water? Because they dont think the Earth could have formed here with all this water - they're right, the Earth formed further out where gases were pushed by the solar wind, condensed and froze in the early nebula. 
