I think I found the line you're talking about. It's not as succinct as you put it, but it gets the idea across.
Steve Rogers:Tony, someone dies on your watch, you don't give up.
Tony Stark: Who said we're giving up?
Steve Rogers: We are if we're not taking responsibility for our actions. This document just shifts the blames.
Yes that'd be it; although I was way off.
I should write movies; my line was much better.