Well, we have two options in tabooing 'compelling'. On the one hand, we could mean 'persuasive' where this means something like 'If I sat down with someone, and presented the moral argument to them, they would end up accepting it regardless of their starting view'. This seems to be a bad option, because the claim that 'there are no universally persuasive moral arguments' is trivial. No one (of significance) has ever held the contrary view.
So our other option is to take 'compelling' as something like what Kantians say about the CI, namely that every mind is committed to it, whether they accept this or not ('not' out of irrationality). As you say, this leaves us with a lot more tabooing and explaining to do. I'm happy to go on with this, since it's the sort of thing I enjoy, but it is a digression from my (perhaps confused) complaint about EY's argument. The important bit there is just that 'compelling' probably shouldn't be taken in such a way as to make EY's point trivial.
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The problem here is that the second option you offer does nothing to explain what a compelling argument is; it just passes the recursive buck onto the word "committed". I know you said you recognize that, but unless we can show that this line of reasoning is coherent (let alone leads to a relevant conclusion, let alone correct) then there's no reason to assume that Eliezer's point isn't trivial in the end. Philosophers have believed a lot of silly things, after all. The only sensible resolution I can come up with is where you take "committed... (read more)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.