Well, the only real terrible thing that Cid had done was go crazy. At least, that's pretty much why he painted him out to be a bad guy. In Balthier's mind, Cid was horrible. Not because of what he had done to the people, but because of what he had done to him. Balthier painted a much worse picture of Cid than what he really was because of his own personal bias. As for Vayne, I didn't really get the impression he wanted to die, but maybe I'll beat the game again and watch for it. As for Venat, I think he realized that the Occurians had their own problems to deal with (such as their self-righteous, religious attitude that they should be worshipped, even though it never gave any clear indication that they had helped in the creating of Ivalice), and realized the only way to make them see this was to break thier grip from Ivalice's destiny. The best way to do this was to make the people of Ivalice realize they had free will, and considering Vayne was in such a position of high power, he seemed like a good choice for Venat to persuade him to break the Occurian bonds.