Steve completely understands all that Carlos is saying, in fact he's not at all in disagreement with him. While he might be fighting for everyone, he doesn't expect that of anyone else, so long as they all strive for the same goal, that's enough to achieve taking down the Capitol.

"I agree, we need to be careful, I don't doubt that to them we are just cannon-fodder, expendable, all I'm saying is I can't see them as the same, but I also don't expect anyone else to share my view," Steve knows that he'll likely be the only one, but he just doesn't have it in him to not fight for everyone. In the war, countries banded together against the Axis powers, so maybe he's stuck in that thinking.

"Caution when dealing with them is smart, they might be our best allies and people I'll fight for, but doesn't mean I trust them," well he doesn't trust half the tributes either, but that's another matter.