Well, call me cautious but its just a matter of time before someone, or something happens and this site gets in the news.....no nothing really is going to help, but forcing any readers to login and register is going to help in a number of ways.
Its going to force folks to go through the process of registering to read, and its going to at least have an over-21 flag on it.
If I owned this site, I'd do it in a second. You can even leave the ads up on the landing page, but when the shit hits the fan, and I said when not if, its going to be a good damage control and an argument that its a private site.....