Actually, technically Steve is last seen being gunned down on the steps of the Courthouse and there was a massive public outpouring of grief after that. Plus Registration turned out to have been pretty useless at stopping any of the problems it was meant to stop so it turns out he was right to fight it.

I can buy that the American people are fine and dandy with him being in charge again. It's a lot more plausible to me than everyone being fine with Tony showing up to that party.