If you're tending such a site as pure art project, fine. However, I suspect the site is there because you envision a community of potential users in this world

If you're tending such a site as pure art project, fine. However, I suspect the site is there because you envision a community of potential users in this world. You are not "forced to register". You are asked by your community to make mutual assurances. The easiest system out there relies on a third party, true. There are other third parties, and you could make your own (the most popular one, you might be surprised to hear, didn't exist a few years ago). And there are other ideas of ways to make this mutual assurance. None have taken off in a big way yet, but I'd encourage you to look to them or think of other ways we could do it! Pretending that we don't need to make this mutual assurance to members of our community is not an option. If you don't like the easy way to do it, find another way.