The anthropic principle lets you compute the posterior probability of some value V of the world, given an observable W. The observable can be the number of humans who have lived so far, and the value V can be the number of humans who will ever live. The probability of a V where 100W < V is smaller than the probability of a V only a few times larger than W.

This argument could have been made by any intelligent being, at any point in history, and up to 1500AD or so we have strong evidence that it was wrong every time. If this is the main use of the anthropic argument, then I think we have to conclude that the anthropic argument is wrong and useless.

I would be interested in hearing examples of applications of the anthropic argument which are not vulnerable to the "depending on your reference class you get results that are either completely bogus or, in the best case, unverifiable" counterargument.

(I don't mean to pick on you specifically; lots of commentors seem to have made the above claim, and yours was simply the most well-explained.)