Regarding the matter of collateral damage, its not just a matter of showing/not showing. Its also how the characters react to it. In the case of Avengers, there is a lot of collateral damage happening. . . and throughout the battle you have various Avengers doing all kinds of stuff specifically focused on minimizing it, from rescuing people from the infantry, to diverting leviathans away from buildings, to tactical plans that explicitly say "keep the fighting contained and focused on us."
Did they prevent everyone from dying? No, but the movie made quite plain that they *did* care. Thus why the fact that they didn't zoom in on giant piles of dead bodies is kind of irrelevant.