Just to avoid this issue, I have a strict rule on my forum that Usernames cannot be changed without good reason, and that posts cannot be deleted without good reason. It really disrupts the flow of a thread if replies are just missing from the overall flow. If people agree to join, then not only will they think twice about what name they want to use, but also think twice about what they say. One of the biggest complaints about the internet is that people say whatever they want because anonymity means no consequences. This makes it more like the real world, where you don't put out there what you don't want coming back to you.