If I were in a crisis, I would be arguing whatever was most likely to convince the other person. If the other person was a moral realist - and most people instinctively are if they never really thought about the issue - then I would argue moral realism. And if the other person was religious - as again most people instinctively are - then I would argue about god. In neither case is that evidence that I believe in moral realism, or in gods; I would just be choosing the most effective argument.

And even if I did believe in moral realism, or the fact that many others do - that is not strong evidence for moral realism itself, because it is explained by evolutionary reasons that made us feel this way. Valid evidence is not that people believe one way or another, but the reasons they can explicitly articulate for that belief. When you observe that most or even all people behave like moral realists under pressure, that is a fact about people, not about moral realism.