Well, Goober, we're just ungrateful bastards. Plus, Fury's a finn, which means by default that he's a crack shot with a sniper rifle. And despite not being Russian and thus not a priority target, it pays to be polite in these kinds of cases.
Besides, I personally don't recall ever being annoyed with you for fixing something, whether it was your mistake or someone else's. Usually I don't even get annoyed at the mistakes themselves, being that they're not deliberate - Humans are, after all, eminently fallible, so it's making sure to clean up afterwards that counts, since never making mistakes just isn't going to happen.