I mean, it's clear that you really want the sniper to have been Bucky. I'm not sure which way I like the story better. Hell, maybe it's a deliberate ambiguity, maybe we're supposed to debate it.
I think, even if we were meant to understand Bucky killed Red Barbarian, that the ambiguity is just an accident/misunderstanding, that his inner monologue is so dissociated from the act is a deliberate choice, and worth commenting on. He's not saying, "I couldn't let this man live, after what he had done." He's saying, "I guess for some people… it falls apart sooner than others." The inability to escape one's past is a huuuuge theme in Brubaker's Captain America work, and that's how that whole monologue is framed. Red Barbarian thinks he can use his money to buy escape from the murky world of espionage, and then the murky world of espionage catches up with him. It's not even that a sniper killed him, it's that his past did. Which is interesting because Bucky's fundamental struggle is navigating his tortured relationship with his own past— and by that logic Bucky is just as doomed as Red Barbarian, in a way. :|a
I read the House of M stuff with Bucky and it struck me as pretty out of character. But it was an AU, so, that was sort of the point. I don't think Bucky's limited to the world of espionage and I think it's a mistake to stick him just in that slot. He's got superheroic tendencies, deep down— his basic M.O. is charging into fights way too big for him and blowing himself up to save the world. I don't think the tragedy of Bucky-as-Captain-America is that he was all wrong for the mantle but tried anyway. The tragedy is that he was right for it, but his Terrible Dark Past keeps him from being the hero he could be. Word got out that he was this communist assassin and so no one would let him be Captain America anymore, despite doing a good job and convincing the hero community he was a worthy successor. And now, obviously, he has to return to this shadow world because the shadow world won't let him operate in the bright colorful one. "No Escape", right? But there's an internal tension there, and a drive to do superhero type stuff, that's just not present in characters like Maria Hill or Nick Fury. And if you wipe out that tension you undercut a lot of what makes his character interesting. Bucky's playing at being James Bond now, but he still wants to save these sleeper guys, not kill them. He has to use the tools of a past he doesn't want to confront the past he doesn't want, but his need to confront that past is kinda his heroic duty. He pretty much said he couldn't have been called Captain America if he didn't take responsibility for all this stuff that's not his fault.