I wasn't making a medical diagnosis...English is a third language for me, but I've been under the impression that "schizophrenic" is an adjective used outside the medical field to describe non-sensical behavior, but I could be wrong. Medically speaking, one of the symptoms of schizophrenia is different forms of thought disorders, which can include illogicality, so the common-usage application of the term, as I understand it, doesn't seem to be completely disjointed from the medical term. Now, I don't want to start pointing fingers here, but there have been complaints by certain people over a certain, not too long, time period, which, when taken together, self-contradict; but again, this is not me handing down diagnoses, but rather describing, in what I perceive as common-use terms, such phenomena.
But back to the topic, some more thoughts:
Regarding the "run eliminateHuman.exe" issue: what if this isn't a bug in the AI but simply a consequence of a combination of the following:
a) the human tending to do well, which, as I've argued many times before, should induce the AI to become hostile toward him to stop him from becoming a runaway (and if you don't like it, again, there's an flag you can set to turn this behavior off),
b) the human being a lot better at war, which quickly leads to more warmonger score and thus hostility (it seems that people who currently find Deity too easy are mostly warmongering, so it seems like more "ganging up on them" and more anti-warmonger bonus is the way to go as the AI will never tactically or strategically surpass the human) and
c) the AI simply being better at diplomacy than the human!
While a) and b) have been discussed before, and a) was "fixed" in the sense that you can turn it off if you wish (but then don't complain about the game being too easy, please), c) hasn't really been mentioned anywhere, but I think it could well be a significant factor. Consider this:
When the human gives commands to his units in a war, there will be an objective standard that could be used to evaluate his actions; while not always easy to determine in a complex game like Civ, theoretically there is a set of "perfect moves" that does not depend on what the AI thinks about them "subjectively". In diplomacy, however, your "moves" are only as good as the AI evaluation of them. Even if you think that you made the "right call" with some diplomatic action, if the AI evaluation of that action is different then you are wrong. Now of course there should be a way for the human to be able to anticipate, to some degree, how the AI evaluates his diplomatic actions, but first of all this shouldn't always be the case (and certainly isn't when the human evaluates AI action; e.g. the AI gives a gift to you, which makes you think "that's nice" but then you declare on them because someone else offers you a lot of Gold or they simply have something that you need that is more valuable to you than their friendship) and secondly I think it's quite probable that the AI puts much more effort into the diplomatic game (who here checks every turn if he can make new deals, DOFs etc. with every AI?) and may also be acting in a more "fine-tuned" manner. I'm not claiming that there couldn't be some bug in the Diplo-AI that makes it pick on the human preferentially, but I think it's quite likely that the situations where the AI gangs up on the human, even though one of them eventually ends up being a runaway with 5 DPs could just be a result of that AI having played a better game, especially on the diplomatic side.
We'll know more after HeathCliffWarrior's diplo debugging enhancements, after which maybe we could look into how to more easily tell the human about "diplomatic opportunities" (e.g. possible DOFs being displayed in the EUI right-hand panel?), but in the meantime it seems that fixing existing bugs (possible "not making improvements"-bug, choosing wrong Pantheons / Beliefs bugs and others) and counteracting warmongers should be the way to go; on that latter note:
How high is the anti-warmonger bonus currently on Deity? Have the people who complained about Deity being too easy tuned this down in their settings? Do they think that more would be better? Or should the AI maybe get production boosts on kill again, but only on high difficulties?
Also, and a similar idea has been "floated" before: what if after the minimum turns for vassalage, enemies of the Vassal's Master, who are Friends with his Vassal, could "sponsor" a revolution by essentially making a special kind of deal with that Vassal AI where the capitulated Vassal becomes the voluntary Vassal of the deal-offering AI (which is a temporary arrangement) and automatic war is declared between the new Master and the old Master for a minimum amount of turns? Additionally, "Iron Fist" could be changed such that it only prevents this, but not the Vassal liberation that can occur after minimum time if the conditions are met (or the other way around). This would counteract a snowballing mechanism that I think is more relevant for snowballing humans than snowballing AIs, since I think the human gets multiple capitulated vassals far more often than the AI.
Lastly, continuing to improve the tactical AI is, of course, the "holy grail" of improvement in this regard, as this doesn't feel "unfair", unlike more bonuses for the AI. However, this is often performance-limited, as well; so what if some more advanced and performance-draining AI tactical reasoning is only available if a certain flag is set, which could be user-chosen or be automatically set to off if the game detects AI processing to take too long? The reason I suggest this is that some people complain about long turn times in late game, which is something that has never been an issue for me; that's likely because I have a fairly powerful machine and I don't really play Huge maps anymore...it seems to me that if you want to play Huge maps or have a mediocre PC / Laptop then you should either accept long turn times or worse AI, rather than the AI being suboptimal for everyone, as long as the average gamer (who typically has a somewhat powerful machine) can still play with full AI and tolerable turn times on standard settings. Perhaps that could enable implementing some AI enhancements that were blocked by performance concerns, but I have a feeling that AI tactical reasoning is probably significantly limited by memory-issues, as well (the old 32-bit problem).