Agreed. Any bug report from a user is valuable - the fact that he was frustrated enough to report it means that there is a problem that needs to be addressed.
Almost everyone files a bug report in frustration because you're filing an issue about something that doesn't work the way you think it should. But most people are considerably more civil about it.
I really don't like to play the "free" card. Too often developers say "well, it's open source so fix it or stop complaining." I don't think that's right at all . . . especially if you've advocated people use your software. However, having been involved with a lot of OSS projects, I can say that the bugs that get fixed the fastest are the ones that affect the developers themselves. Anything that gets fixed above and beyond that is a developer being a nice person in volunteering his time to help someone else. More to the point: it's hard to get people to work for free when they're demoralized and bug reports like this are demoralizing. If I were involved with the project, he's about the absolute last person I'd try to please no matter how right he may be.
So, while I'm neutral on the ban, the bug reporter has to realize this is a very ineffective way to win friends and get his issues resolved.
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.
