This seems to really reason through only the happy path, ignoring bad actors, and there'll always be bad actors.

True, but the bad actors can defeat any security mechanism you put in place with a proxy, or a copy'n'paste, so the downside risk is pointless worrying about. The upside of allowing traffic is that your content that you presumably want people to read can be read by more people. For all but the most popular blogs that's probably a net benefit.