Before travelling much further, let me make sure that we keep this discussion in its context.
Assume that you are an intentional agent with desires, surrounded by a community of intentional agents with desires.
Desires - expressed in the form "desire that P" where P is a proposition - motivate agents to realize states of affairs in which the propositions that are the objects of their desires are true.
As I have argued, you have four ways to cause other agents to choose actions that would realize the propositions that are the objects of your desires.
If one of those agents has a desire that Q, you could:
(1) Bargain: "If you help me to realize P, then I will help you to realize Q".
(2) Threaten: "If you do not help me to realize P, then I will act so as to realize not-Q".
(3) Alter beliefs: "You can most efficiently realize Q through actions that will have, as a side effect, the realization of P."
(4) Alter desires: Give the person with a desire that Q a desire that R that will, given his beliefs, motivate him to act in ways that will realize P.
I have asserted that morality has to do with method (4). Specifically, morality is concerned with the use of rewards in the biological sense (such as praise) and punishments in the biological sense (such as condemnation) to trigger the reward-learning system to adjust desires.
A good desire - or a "virtue", in this sense - is a desire that people can and generally have many and strong reasons to create or promote using these tools. A "vice", on the other hand, is a desire that people generally have many and strong reasons to inhibit or extinguish using these tools.
I should also extend this to cover the concepts of moral obligation, non-obligatory permission, and moral prohibition.
A "moral obligation" is an act that a person with good desires (a virtuous person) would perform.
If an agent performs this action, we have at least prima facie evidence that the agent has those desires that people generally have many and strong reasons to create or promote, and lacks those desires that people generally have reasons to inhibit or extinguish.
The tools for creating and promoting this virtue in others involve using rewards (such as praise). The virtuous person - the person who does what he ought - gets praise and reward, as a way of encouraging like desires in them and in others who are a witness to these rewards and praise.
On the other hand, the person who does not do what he ought - who shirks an obligation - is to be subject to what are punishments in the biological sense, which includes moral condemnation.
But, remember, an obligation is not what people actually praise others for doing and condemn them for not doing. It is what people have the most and strongest reasons to praise people for doing and condemn them for not doing.
People - even whole cultures - might be wrong about what they have reason to praise or condemn, as with a group who thinks that eliminating a certain disposition in others (homosexuality) is necessary to prevent widespread suffering at the hands of an evil and malicious deity.
A moral prohibition, on these same terms, is an act that a person with good desires would not perform. Of an agent does perform such an act, then it follows that the agent either lacks certain virtues, or has certain vices. People generally have many and strong reasons to bring the social tool of punishment (in the biological sense - which includes condemnation) to bear against such individuals. This serves to trigger the reward-learning system to inhibit the relevant desires or promote the virtuous aversions that would then cause people to choose not to perform similar actions.
Between these, we have the realm of non-obligatory permissions.
I cannot simply use the term "permission" here because "permitted" means "not prohibited" - and even obligatory actions are permitted. However, obligatory actions do not exhaust the realm of that which is permitted.
My decision to write this post, for example, is permissible, but not obligatory. I have a non-obligatory permission to eat oatmeal for breakfast, or to have some of the leftover pizza instead.
The fact is, there are some desires that we have reason to want some people to have, but not all people. A variety of desires, in some areas, reduces conflict and produces a mutually beneficial harmony.
One clear example of this are desires related to the choice of a job. Rather than having everybody want to be engineers and trying to get some to live the disappointed life of a teacher, we get better social harmony and desire fulfillment if some people liked engineering and others liked teaching. So, the professions of engineering and teaching fall into the realm of non-obligatory permissions.
We reduce competition and conflict as well if we like different foods. What to eat tends to fall into the realm of non-obligatory permissions. What we do for entertainment fits that category.
In all of these cases, we can certainly find a subset that is morally prohibited. "Burglar" is not a morally permissible profession because people generally have many and strong reason to use rewards and punishments to promote an aversion to taking the property of others without consent. I think we have many and strong reasons to promote an aversion to eating human flesh, and to entertain oneself with child pornography.
However, the existence of some prohibitions in this realm does not disprove the claim that there is also, within this realm, a vast area of non-obligatory permissions. And the reason for non-obligatory permissions is because there are some desires we have no particular reason to make universal or to extinguish using those social tools that touch on the reward-learning system.