It wasn't really an argument, but this wasn't the first time that Steve had admitted to thinking that it should have been him to go, that he should have made that sacrifice. And it was only because he said it like he did that Tony didn't push back, didn't say that it never could have worked that way because Tony wouldn't have allowed it. Hadn't, in fact.
"Oh," he said, quiet and biding his time while he tried to comprehend, to find the words he needed to get some of that guilt off of Steve's shoulders because it was a silly place for it to be. He reached up, carefully thumbed away the tears on his cheeks -- Steve cried quiet, there was no show to put on, no attention he was trying to garner. Just a sadness he couldn't quite hold back.
"I would have anyway. You have to know that. There's no such thing as getting out for good, not for people like us." Well, except death, he supposed. But that wasn't really the point. The point was that it didn't matter that Steve felt like he'd pressured Tony. Eventually he would have come around anyway, because that was what he did. It was what he always did.
And he was certain that even with what Tony knew he had at that point, it wasn't everything he wanted. There was Pete. A whole universe broken. He'd never have been so selfish as to just ignore it, not even to be able to get to keep what he'd built for himself. He'd always been too much of a mechanic to not try and fix everything. "Gimme some credit," he said, covering Steve's hand over the reactor with one of his own. "It was the whole damn universe, not the world." It was never not the time for a sassy remark, apparently.