Which would have been a big bang with as many minor characters dead as possible. Instead they "only" killed Andrea. Well, and Milton.
As for the Governor shooting his own people: it may seem stupid and did ruin his chances of ever taking the prison, but fact is that they just got their asses kicked and people started talking back at him, something he did not really have to deal with in Woodbury except for Andrea. So it was very much in character for him to react that way. For me, that made him look even more of a threat, at least when encountering him alone because he just gradually turned more and more nuts.
I really wanted him to be taken down in this finale, but I am fine with him sticking around as the villain next season as well.

As for Carl...I am not really comfortable with someone explaining or justifying his shot just because the kid handed over the gun weirdly. And I think even a show about the zombie apocalypse has to keep the moral higher ground and show that it is never ever cool to shoot a teenager who is not a walker yet.
That being said, I agree that Carl is simply adapting to the world he lives in now but probably won't be turning evil anytime soon. After all the things he saw his dad do and say it is no surprise that he toughens up.