It bears repeating.
So you've noticed you can't justify your moral intuitions. (Nihilism is true, naturally you can't.) You can't possibly do anything as silly as adjust your ideology, that would be admitting you were wrong about something. Instead have to figure how to make sure nobody notices. (Paging Sailer...) Anyway, the point is to make friends, right? You can make lots of friends by conspicuously avoiding the whole justification issue, since they've noticed the same thing and don't want to deal with it any more than you do. When we choose to use a word, it means what we want it to mean, neither more nor less, and that's that! Plus, if you adjust your ideology, it won't be the same ideology as all your friends anymore. You might become less popular.
Justifying your moral intuitions is abstract theorizing, which is metaphysics. (Naturally, noticing this equivalence is also metaphysics.)
Metaphysics isn't real. Every modernist says so, it must be true.
Thus we say nobody should think abstractly if there is any way to avoid it.
And thus we can call ourselves nihilist without having to suffer the inconvenience of knowing what nihilism is. Handy!
Also, if you had any fucking clue what you were talking about, then you'll make the clueless feel envy and jealousy. That's morally wrong.