Remove ability to change username

Quite simply, there are a minority of users - some legitimate, some trolls - that seem to constantly change their usernames. It is detrimental to the site overall for people to be able to do this and avoid being put in the context of their previous opinions. You also should not be able to create sock puppet accounts - one post I read earlier said the person would log into each of their five alternate accounts and give MS to this particular person, and lo and behold, exactly 5 MS was given on an otherwise innocuous post. Please take measures to stop this.