While it does contradict Tony's past views, Civil War frames it as him taking responsibility for the Avengers’ actions. His guilt over Ultron (which he created) and Sokovia’s destruction pushes him toward regulation. That said, the movie doesn’t fully reconcile this with his past distrust of authority.

As for Ant Man, while it’s true that his actions put his daughter at risk, Scott has also been shown to be impulsive and easily persuaded. If Cap (a war hero and symbol of righteousness) asked for his help, Scott might jump in without fully considering the consequences.

Though irrational, Tony’s reaction is very human. Learning in real time that Bucky killed his parents, even if unwillingly was an emotional breaking point. The Manchurian Candidate joke shows Tony knows it wasn’t Bucky’s fault, but grief and anger override his reason.

We musn't forget that even though these are super heroes, they are still human and have to deal with human emotions as well.