I think it's more complicated than that - after all, most if not all the characters in HP don't fall into categories of "good" and "evil" - there are several layers of grey area. However, I do believe he killed Dumbledore for the right reasons, and that there's more to him than we already know - particularly concerning Lily and his motivations for joining the Order. I also believe Dumbledore would have needed more than an apology to be able to trust him - possibly an unbreakable vow.