I think you put your hand solidly on the dull end of the stick here. Lets consider some other moral examples whos violation does come up in real life.

1) I ought not steal candy from Walmart, but its OK if you do.
2) I ought not steal the entire $500,000 retirement from someone by defrauding them, but its OK if you want to.
3) I ought not pick a child at random, capture them, hold them prisoner in my house, torture them for my sexual gratification, including a final burst where I dismember them thus killing them painfully and somewhat slowly much to my delight, but its your choice if you want to.
4) Out of consideration, I won't dump toxic wastes over my neighbors stream, but that's just me.

My point is, the class of "victimless crime" types of morality is a tiny subset surrounded by moral hypotheses that directly speak to harms and costs accruing to others. Even libertarians who are against police (relatively extreme) are not against private body guards. These libertarians try to claim that their bodyguards would not be ordered to do anything "wrong" because 1) morality is real and 2) libertarians can figure out what the rules are with sufficient reliabillity and accuracy to be trusted to have their might unilaterally make right.

So that's my point about the philosophical basis of moral realism. Does that mean I would NOT enforce rules against dismembering children or stealing? Absolutely not. What it means is I wouldn't kid myself that the system I supported was the truth and that people that disagreed with me were evil. I would instead examine the rules I was developing in light of what kind of society they would produce. MOST conventional morality survives that test, evolution fine tuned our morality to work pretty economically for smart talkative primates who hunted and gathered in bands of less than a few hundred each.

But the rest of my point about morality not being "real", not being objectively true independent of the state of the species, is that I wouldn't have a fetish about the rightness of some moral conclusion I had reached. I would recognize that 1) we have more resources to spend on morality now than than what with being 100s of times richer than those hunter gatherers, 2) we have a significantly different environment to optimize upon, with the landscape of pervasive and inexpensive information and material items a rather new feature that moral intuitions didn't get to evolve upon.

My point is that morality is an engineering optimization, largely carried out by evolution, but absolutely under significant control of the neocortexes of our species. The moral realists I think will not do as good a job of making up moral systems because they fundamentally miss the point that the thing is plastic and there is in most cases no one "right" answer.