It sounds like you agree with me, but are just using the words morality and nihilism differently, and are particularly using nihilism in a way that I don't understand or that you have yet to explicate.
It also seems to me that you're already talking about what you value when you talk about desirable worlds.
That's my point. You're saying the 'nihilists' are wrong, when you may in fact be disagreeing with a viewpoint that most nihilists don't actually hold on account of them using the words 'nihilism' and/or 'morality' differently to you. And yeah, I suppose in that sense my 'morality' does tie into my actual values, but only my values as applied to an unrealistic thought experiment, and then again a world in which everyone but me adhered to my notions of morality (and I wasn't penalized for not doing so) would still be preferable to me than a world in which everyone including me did.
I have noticed that the term 'nihilism' has quite a few different connotations. I do not know that it is a coincidence. Reputedly, the most popular connotation, and in my opinion, the least well-defined, is existential nihilism, 'the philosophical theory that life has no intrinsic meaning or value.' I think that most LessWrong users would agree that there is no intrinsic meaning or value, but also that they would argue that there is a contingent meaning or value, and that the absence of such intrinsic meaning or value is no justification to be a generally insufferable person.
There is also the slightly similar but perhaps more well-defined moral nihilism; epistemological nihilism; and the not-unrelated fatalism.
Here, it goes without saying that each of these positions is wrong.