I think it's more about the principle of the thing. It's definitely a bad thing to have satellites up there that no one knows are there (because of collision r

I think it's more about the principle of the thing. It's definitely a bad thing to have satellites up there that no one knows are there (because of collision risks, etc.), and the US not registering theirs opens the door for other nations/entities to see what we're doing and choose to do the same, which would be bad for everyone.