They don't, but they will be. If for no other reason than the concrete knowledge that somehow your alias on a site is verifiably connectable to person X will le

They don't, but they will be. If for no other reason than the concrete knowledge that somehow your alias on a site is verifiably connectable to person X will lead to a raft of abuses of the legal system to silence or harass people saying things someone doesn't like. And average sites aren't going to have the resources or will to fight this.