Namor was possessed by the Phoneix in AvX, so he gets a bit of a pass there. And in all fairness the Squadron is USUALLY mind controlled (or possession or something along those lines) when they do something which requires the Avengers to stop them too. But it's a rare case where the Squadron wasn't actually mind controlled and were just asking the way they were just because. No free pass there... hence them getting chased down by SHIELD and the Avengers.
Even the Squadron themselves realize that what they did was wrong in the end. They screwed up, they realized they screwed up, and they tried fixing it... hence afterwards SHIELD and the Avengers let the Squadron be. They weren't villains... they were just being stupid, and everyone in the end let it slide. It just took the Squadron a little while to get there, that's all.
As far as the path being to stop the Myriad... if they had actually done anything to stop the Myriad then we'd be having a very different conversation right now. Problem being that's not really the case. Again, apart from Weird World they did nothing but fight other heroes. They're even picking fights with heroes who weren't actively chasing them, like Blue Marvel. They attacked the lab he was working with for no aparent reason, got their butts kicked, and that was that. They accomplished little to nothing, realized that, and went their seperates ways. Unless the Myriad was operating on the streets of Chicago, I'd say the Myriad fiasco just illustrates how relatively big a flop this team ended up being. If stoppng the Myriad was their path, then how much credit do you realistically expect any reader to give them based on that?