For the sake of the discussion, let's suppose that morality is not a spook. Then tell me...

For the sake of the discussion, let's suppose that morality is not a spook. Then tell me, Veeky Forums: why should I be moral?

so you don't get anally raped in prison

Not a Stirnerfag but Morality is such a nebulous and impossible-to-objectify concept that it ought to be abandoned entirely in favor of preservative Ethics.
At least then one can have an empirical argument of formal theory. Unless you accept some unfalsifiable (or worse ideology-driven metaphysical) Platonic notion of Good, you can't quantify Morality in any meaningful way.

Morality is a benelovent self-imposed restriction people use to make sense of the world. Just like we use logic to structurize the external reality, we use morals to regulate our mind. You don't seem to be asking questions like "Why should I act logically? Why can't I just eat my shit and bang my head against the wall?"

Consider that fact that we have assumed morality is not a spook. Therefor because morality is not a spoke you should be moral.

morality is a product of evolution
you ask why you should be moral as if you have free will. whether or not you behave morally or immorally is a reactive outcome.

99% of people here are anti-realists about morality, so this isn't really the best place to ask. Anyway, if one is a moral realist, then the reason you ought to act morally is because morality is, by definition, what one ought to do. So, you ought to do what you ought to do. Some ethical theories, like virtue ethics, provide a more direct benefit to the person; aka, under virtue ethics, you ought to do what makes you a virtuous person and contributes to flourishing, and virtue and flourishing are Goods unto themselves.

/thread

Because it's good.

Out of self-interest. Being moral (adjusting to accepted social norms) will make you accepted and successful in your particular social group, and may result in reciprocal acts.