To be honest, I don't see what the problem is. In Britain games have been rated by PEGI as an advisory authority, like your ESRB, but also the BBFC rates games too. Although the PEGI ratings are somewhat more informative, the BBFC ones are legally binding. Hence, a game published in Britain that is PEGI 15 can be legally sold to under-15s, although most shops won't do so. But a game rated BBFC 18 cannot legally be sold to under-18s. Although legally sold is different to legally played. So yes, generally I don't see the problem. We get along just fine and dandy here. If you want a game rated higher than your age, you beg your parents who (should) make an informed decision.
This system doesn't restrict our free speech - there is nothing stopping people from making these games, only a legal penalty for people who sell 18-rated games to children directly, which I think is fair enough. All it takes is one check of a Driver's License (I work in a shop where we sell games, so I do it regularly).
The much bigger problem we have here in Free Speech is our damned libel laws
(Note: in general games not rated 18 will be rated by PEGI only, or at least show only the PEGI rating on the box, although the BBFC is still required to rate them and will give information on it's website. Because the BBFC rating is not on the box, it is not required to be enforced, this is why a game that is PEGI/BBFC rated 15 can still be sold to under-15s legally as the BBFC rating does not appear on the box. They only put the 18 BBFC rating directly on the box, because as before mentioned, industry self-regulation through PEGI is pretty good, they just want to enforce a penalty on the "worst stuff" - i.e. BBFC 18.)