Would it of not been a bigger risk to move, knowing AAF would turn innocent?I agree with you that UN doesn't seem as likely to be scum after that but that does not excuse his scummy posts. The mafia being willing to take that big of a risk on Day 1 does sound unlikely though.
We also have to take into account that the scum team still has one more hit that they now get to use on whoever they want. The rules are the same as when they were posted in the signup so there may only be 3 members of the mafia team which makes more sense to me. If there are 4 people on the mafia team, odds that the town would win were never good to begin with.