Theaters don't like 3 hour movies. It means they can't get in as many showings, which means the movie ultimately loses money. A bunch of theaters and distributors were bitching at Disney when Pirates of the Caribbean 3 came out, because they felt the increased length was costing them money.
Thor and Captain America kill people in the movies but Thor and Captain America both kill people in the comics anyway. A refusal to take lives isn't a major part of their characterizations like it is for Batman and Superman. Cap killed people from the very beginning, and barring a stretch in the 80's where writers claimed he'd never ever killed anyone before, he seems mostly fine with it. He's a soldier. Knowing that he might have to end the lives of his opponents is something he knows full well.
Superman is about being better than that. Superman would have found another way. People can whine about it being self defense but the fact of the matter is he's not real. He killed someone because the writers chose to make him a murderer, just like they've chosen to depict him as a wooden, dour bore of a man.
And Clark saying a human could survive being driven through walls like that just shows this (per)version of Clark is an idiot on top of being a murderer and boring.