Perhaps I am not understanding things here.
"can’t have a moral theory that says that desires are the primary object of moral evaluation without a theory of desires."
Just because your argument can be expressed does not mean that the concept has merit by any or my philosophical system, no matter how much is written about it or how well it is written.
Once we have settled on a ethical system that seems right and feels right, all new systems are tested against that system, and any found lacking are rejected. That is the process of ratcheting to the best system of the day. From that we can define a set of virtues to live by and we do not need to employ our time consuming reasoning but employ or rapid automatic portion of thinking. Away we go. Desire does not even come close to primary object of moral evaluation in my understanding of life. Life is the primary object of my moral evaluation, and from what I can see, is for most of the philosophers of life sorts.
Well, all this does not matter, for this is the internet. It is a place for expression, not facts. The truth is elusive, and we must test each statement against our previous accepted knowledge. It it does not match, just reject it, without more evidence. Cognitive dissonance is also not good. We have three choice, reject, assent, or hold in abeyance. Abeyance just takes too much memory.
There is a related issue also. Most professionals will not listen to non-professionals... people of lesser standing... well perhaps not, that point out something that may make the professional wrong. CDC will not look at data that suggests one of there proclamations are wrong, food guys with their food pyramid, the same "we are always right" attitude, big ego attitude, Monsanto and GMO, chemicals, Autism Speaking, and their funding controlled message, Autism Spectrum lumping all the autism's together into one, yet there are at least four desperate issues, Diagnostic and Statistical Manual of Mental Disorders version 5 (DSM-5), and the same issues with eating disorders.
Some of the time the data is right and the organization is wrong. There is one principal that keeps those organization in ignorance, "contempt prior to investigation."
But what do I know?