Yep, exactly. Any serious person can eventually get to the conclusion that morality isn't objective. I'm not sure I could claim that anything is truly objective. But that doesn't mean that there's no such thing as a meaningful morality. Or that its subjective nature means that our moral standards are meaningless.

The same goes for social norms in my book. There's lots of stuff around the edges that we can have good faith disagreements about. But some norms, like not threatening strangers (or at least not being surprised to get jumped if you do) seem pretty uncontroversial to me.