Considering the extreme is only useful if the extreme is a realistic one -- if it is the least convenient possible world. (The meaning of "possible" in this sentence does not include "probability 1/3^^^3".) With extreme Omega-scenarios, the argument is nothing more than an outcome pump: you nail the conclusion you want to the ceiling of p=1 and confabulate whatever scenario is produced by conditioning on that hypothesis. The underlying structure is "Suppose X was the right thing to do -- would X be the right thing to so?", and the elaborate story is just a conjurer's misdirection.

That's one problem. A second problem with hypothetical scenarios, even realistic ones, is that they're a standard dark arts tool. A would-be burner of Dawkins' oeuvre presents a hypothetical scenario where suppressing a work would be the right thing to do, and triumphantly crows after you agree to it, "So, you do believe in censorship, we're just quibbling over which books to burn!" In real life, there's a good reason to be wary of hypotheticals: if you take them at face value, you're letting your opponent write the script, and you will never be the hero in it.