Surely typical moral realists, atheist or otherwise, don't believe that they've got the correct answer to all possible moral problems.

Apparently I mis-stated something. I'm a little too spent to fully rectify the situation, so here's some word salad: moral realism implies belief in a Form of the Good, but ISTM that the Form of the Good has to be personal, because only intelligences can solve moral problems; specifically, I think a true Form of the Good has to be a superintelligence, i.e. a god, who, if the god is also the Form of the Good, we call God. ISTM that belief in a Form of the Good that isn't personal is an obvious error that any decent moral philosopher should recognize, and so I think there must be something wrong with how I'm formulating the problem or with how I'm conceptualizing others' representation of the problem.