Aside from the concept of adults masquerading as non-adults, nothing so long as those spaces are moderated fully. I have no problem with skipping the verification, but I do question the moderation of most services.

The problems start when the space become not-for-children and identity validation is mandatory to use them, which will exclude people like me who categorically refuse to hand over personal secrets in order to have access. It does not warrant the inherent risk involved with granting access to personal details unrelated to the service offered. I reckon this will happen when someone decides it's better commercially to make a service adult-only than to moderate non-adult accounts. It's a slippery slope, and a predictable next step once adult have become accustomed to handing over papers for some services to have to do it for many, if not all.