Then you play a different game than I do. The AI is stupid and has no real gameplan, I agree. But they do NOT gang up on you. Unlike CIV2 and Sid Meier's Alpha Centauri. They also DON'T pass free techs around.
I have played many games where they attack each other in the early game.
This Sid level SG is just one of the examples I can show you. The early war between two civs was one of the main reasons for our win.
This is true. Sadly this bug hasn't been removed every since vanilla civ. Otoh you can profit from it. When an AI crosses my lands to settle near future resources I often let them. This will be one of MY future cities. But I guess that's not your point.
The attitudes of the AI vs you are hardly important. Sure, they determine their potential UN vote, but that vote is easily manipulated. I agree that Democracy is hardly useful and that attitude says nothing about the willingness of the AI to attack you. Just don't play a game trying to please the AI.
Yes. This happens on higher levels. One of the features of levels above regent is that AI buys and sells their goods below 'marketprices' to another AI. Another feature of the higher levels is that they can build improvements for less shields. Below regent the human has the advantages. Regent is the most honest level.
This depends on the type of civ you are up against. Less aggressive civs tend to like you (France, India) and more aggressive civs tend to hate you (Zulu, Mongols). But one thing is clear: the bigger you are, the more they hate you. Simple game mechanics, as in
Bamspeedy's AI-attitude article
The AI will do anything when the price is right. They also are willing to trade with you while they are planning to sneak attack you. The AI is stupid and bases their deals on short term economics gains.
You are right that Republic and Democracy are similar to each other. My conclusion is different though. I consider Republic to be the best government in almost all situations and Democracy not worth the anarchy.
I can understand that you are frustrated about the AI. But you mix up facts and myths here.