People own their own creations. The power owns (the copyright on) his comment even if he posts it to your blog, unless you've made an agreement otherwise (e.g.

People own their own creations. The power owns (the copyright on) his comment even if he posts it to your blog, unless you've made an agreement otherwise (e.g., in your blog's terms of service). You control what your blog displays, though. There is probably a technical legal difference between deleting a comment (definitely right and legally permissible) and modifying a comment (thus creating a derivative work of a copyright work which you may not be licensed to derive from).