Let me try using an extended metaphor to explain my point: Remember Eliezer's essay on the Pebblesorters, the aliens obsessed with sorting pebbles into prime-numbered heaps?

Let's imagine a race of Pebblesorters that's p-morality consists of sorting pebbles into prime-numbered heaps. All Pebblesorters have a second-order desire to sort pebbles into prime-numbered heaps, and ensure that others do so as well. In addition to this, individual Pebblesorters have first order desires that make them favor certain prime numbers more than others when they are sorting.

Now let's suppose there is a population of Pebblesorters who usually favor pebble heaps consisting of 13 pebbles but occasionally a mutant is born that likes to make 11-pebble heaps best of all. However, some of the Pebblesorters who prefer 13-pebble heaps have somehow come to the erroneous conclusion that 11 isn't a prime number. Something, perhaps some weird Pebblesorter versions of pride and self-deception, makes them refuse to admit their error.

The 13-Pebble Favorers become obsessed with making sure no Pebblesorters make heaps of 11 pebbles, since 11 obviously isn't a prime number. They begin to persecute 11-Pebble Favorers and imprison or kill them. They declare that Sortulon Prime, the mighty Pebblesorter God that sorts stars into gigantic prime-numbered constellations in the sky, is horribly offended that some Pebblesorters favor 11 pebble piles and will banish any 11-Pebble Favorers to P-Hell, where they will be forced to sort pebbles into heaps of 8 and 9 for all eternity.

Now let's take a look at an individual Pebblesorter named Larry the Closet 11-Pebble Favorer. He was raised by devout 13-Pebble Favorer parents and brought up to believe that 11 isn't a prime number. He has a second order desire to sort pebbles into prime-numbered heaps, and a first order desire to favor 11-pebble heaps. Larry is stricken by guilt that he wants to make 11-pebble heaps. He knows that 11 isn't a prime number, but still feels a strong first order desire to sort pebbles into heaps of 11. He wishes he didn't have that first order desire, since it obviously conflicts with his second order desire to sort pebbles into prime numbered heaps.

Except, of course, Larry is wrong. 11 is a prime number. His first and second order desires are not in conflict. He just mistakenly thinks they are because his parents raised him to think 11 wasn't a prime number.

Now let's make the metaphor explicit. Sorting pebbles into prime-numbered heaps represents Doing the Right Thing. Favoring 13-pebble heaps represents heterosexuality, favoring 11-pebble heaps represents homosexuality. Heterosexual sex and love and homosexual sex and love are both examples of The Right Thing. The people who think homosexuality is immoral are objectively mistaken about what is and isn't moral, in the same way the 13-Pebble Favorers are objectively mistaken about the primality of the number 11.

So the first and second order desires of Larry the Closet Homosexual and Larry the Closet 11-Pebble Favorer aren't really in conflict. They just think they are because their parents convinced them to believe in falsehoods.

I am having trouble seeing a significant difference between that and what you've described. Mimi's enabler could argue "human happiness is a Good Thing unless it seriously interferes with some other really important goal," and then one would have to make the engineering judgment of whether heroin addiction and homosexuality fall on opposite sides of the "serious interference" line.

Again, I assumed that Mimi was a psychologically normal human who had normal human second order desires, like having friends and family, being healthy, doing something important with her life, challenging herself, and so on. I assumed she didn't want to use heroin because doing so interfered with her achievement of these important second order desires.

I suppose Mimi could be a mindless hedonist whose second order desires are somehow mistaken about what she really wants, but those weren't the inferences I drew.

Mimi's enabler could argue "human happiness is a Good Thing unless it seriously interferes with some other really important goal,"

Again, recall my mention of a hypothetical Heroin 2.0 in my earlier comment. It seems to me that if Heroin 2.0 was suddenly invented, and Mimi still didn't want to use heroin, even though it no longer seriously interfered with her other important values, that she might be mistaken. Her second order desire might be a cached thought leftover from when she was addicted to Heroin 1.0 and she can safely reject it.

But I will maintain that if Larry and Mimi are fairly psychologically normal humans, that Mimi's second order desire to stop using heroin is an authentic and proper desire, because heroin use seriously interferes with the achievement of important goals and desires that normal humans (like Mimi, presumably) have. Larry's second order desire, by contrast, is mistaken, because it's based on the false belief that homosexuality is immoral. Homosexual desires do not interfere with important goals humans have. Rather, they are an important goal that humans have (love, sex, and romance), it's just that the objective of that goal is a bit unusual (same sex instead of opposite).

EDITED: To change some language that probably sounded too political and judgemental. The edits do not change the core thesis in any way.