That's not strictly true. If you've already got a report of the issue from other more helpful users, then someone coming in and calling you names and threatening to physically harm you, that isn't necessarily adding value.

We're very fortunate at Mozilla to have tens of thousands of but reporters who aren't bullies and who don't think because they wrote some GNU code once that they can threaten you and deride you. This means that the cost of kicking out the bullies is either trivial, or a net win.