I'm not talking about being able to edit your posts after you post them. Allowing us to do that would be bad, because there'd be discontinuities in the conversation if someone went back to their original post and changed it, confusing readers as to how such a conversation was produced in the topic.
I'm talking about deleting posts. We ought to be able to delete our own topics (if no one has posted in them) and delete our own (non topic-creating) posts at any time. If we just have this feature, we'll be able to take back mistakes without creating any discontinuities or confusion in the conversation.