Please continue using GitHub as you were, but maybe consider acting on your words and either removing or changing licenses within your code that does not represent your ideals. Nothing is preventing you from releasing code into the public domain, so do that!
Is this true? Is there really a large portion of contributors speaking up against this? I got the opposite sense, that it was a very small portion of contributors speaking up against this but I don't have any evidence one way or the other.
No, that's your opinion, which as it turns out also has no legal basis. For me, I want proper attribution from people who use my code. And for any code that I release that's under copyleft, I absolutely do want that license followed.
You seem to be fine releasing your stuff into the public domain, and that's great that you want to do that, but you don't speak for everyone.
Not everybody is and that's ok too.
However other people for varying reasons have other ideas ...