The Genesis account is meant to be an allegory of what has happened to the Human race. It is not meant to be a history. And it applies to all of Humanity. It is not one single event, but a series of events that transpired with different actors, but with similar motives and effects.
But what
evidence do you have to support this contention? Religious texts the world over include allegories of events affecting the human race, the difference here is that this 'allegory' is used to explain and justify an actual, physical change to humanity (humanity used to be immortal, not subject to death or disease FFS!), yet you expec people to accept it on simple 'say-so'.
If something actually happened to humanity that made us subject to death when we were previously immortal then it is the single most important event in history and we should have some evidence of its existence - not just an unsupported assertion.
Of course, the other option is that it is just an allegory, a myth. But it inevitably then follows that Original Sin is also a myth or allegory. And that gets us into difficult territory for the church - if Original Sin is not real then the Problem of Evil is insurmountable and God is either not real or not as the Bible describes Him, and Jesus did not die to save us.
Thus the whole philosphical structure of Christianity depends on something being accepted which is both a myth and yet real simultaneously - not a problem two hundred years ago when people didn't know that the Adam and Eve story was a myth, but a massive problem now, if only people would consider the church's proposition rather than accepting it without question...
It supported the massacre? Considering how set the culture of Human Sacrifice was in ancient Aztec society, regardless of whether the Church indeed supported the massacre, one could still argue that the massacre was 'necessary'. God's Laws are immutable, and God has said that it is right to raise arms, if only to prevent greater evil from transpiring, in this case, the continuation of Human Sacrifice.
Was every inhabitant of south and central America a heart-rending aztec sacrificer? Of course not, and you know it. I'm frankly staggered that you are trying to defend religious genocide.
Have you even studied the Church's statements with regards to its stance in the moral issues you have enumerated? Call the Church dogmatic if you will, but never make the accusation that it is irrational and unreasonable.
Yes, I have studied the basis of at least some of their assertions (e.g. action on AIDS), and I would go beyond irrational and unreasonable toward irresponsible at best, totally immoral at worst.
For example, the Vatican has knowingly invented and promulgated 'science' that it knows is false in order to persuade the faithful (and other unfortunate people) not to use condoms, despite not a single piece of scientific evidence to support their contention. As a result they
condemn people to die rather than accept that their moral contention (condom use is wrong) leads to an immoral outcome (lots of people die unnecessarily due to following church teaching, lots of children are orphaned, and themselves die of poverty & malnutrition).
Actually, describing the church's actions in this area as immoral is understating the case - frankly it is downright evil.
I think you should find out more about the Church's actions before trying to defend them...
All the best
BFR