My policy owes a great deal to John Scalzi’s excellent example.
This is my site. On it, I say what I like. You are not required to like my opinions. (Sometimes I don’t even like them.) I reserve the right to moderate comments as I see fit and to ban whoever I please. There is a vibrant comment culture here, which I love, and to keep it nice for everyone (most of all for myself) I will not hesitate to use a Hammer of Sweet Justice.
I also reserve the right to post, with full identifying information, threats to myself or to anyone else. At the very least, such threats deserve to be mercilessly mocked.
I very rarely have to invoke these policies, and I’d like to keep it that way. Most of my Readers and commenters are lovely people who I would not hesitate to bake pies for. This is the Internet, though, and there’s always a few bad apples. Who have been warned.