My headcanon is that Nat isn't on Tony's side because of Tony, she's actually on Pepper's side, because she was friends with Pepper before she was friends with Steve.
My thing with Nat (and ink-phoenix and I were talking about this one the phone the other day) is that she’s shortchanged in pretty much every film ever. Even though she’s not a love interest in TWS and yes, she does have some amazing moments of her own, she is still very much there to support Steve’s story, which is why the idea of her siding with Steve (or Tony via Pepper) irks me as it currently stands. It’s that it once again sets her on a path that is defined by her relationship to someone else and what she can do for them, not because it is a decision we have seen her come to on her own.
The other Avengers are a little different, but Nat is the one character who has spent a significant time with both Steve and Tony and who you could legitimately argue might go either way on the topic for her own personal reasons,. But we haven’t had enough character development from her for any choice she makes to be 100% about her and not just which teammate she is siding with or against.
Tell me she’s siding for the legislation because she’s been betrayed by the system she thought was fighting for good and she wants to see a greater level of accountability in place because yes, the likes of SHIELD will always be necessary but they NEED to have controls in place.
Tell me she’s siding against it because she’s been betrayed by the system she thought was fighting for good and she doesn’t trust any governing body to act without some level of corruption and she’s done being used by people.
Tell me something, and then show it to me. Don’t just say ‘she’s on Tony’s side’ or ‘she’s on Cap’s side’ because that’s just a cop out and I am sick and tired of seeing her be used as a prop with lines when she is so much more.
I ranted, I apologize. Please don’t think I am aiming this at you personally!