DeviantART do a similar thing with their content where in order to view mature 18+ material (gore, sexual, drug, etc) you have to be a member and then allow that content to be viewed. From what I can tell from when I used the site years ago it never really affected their advertising and I never, and still haven't, seen ads that push the realm of acceptable.

So as what HeySeuss said, if you block it up in the right way its going to keep the community happy with their privacy as well as protect some of our younger members.