Grouping people like that sounds neat, but is the idea that their posts would be visible to other radical people, or would be invisible to everybody?
Because if it's the former, I'm sure some people (I'm not saying me, but probably me) would rather take pride in being put into that sort of 'elite club'. Maybe not necessary with a small community that you have here now, but with a bigger one, there would be people who'd intentionally try to get censored.
And if it's the latter, well, I fail to see the difference between that and regular ban+post removal.
... Please don't post that anywhere. I have no idea what rules it breaks but it must break some. ;_;
Anyway, the second thing I was thinking it would be visible to all the radical people. But that was a joke, and it doesn't work well in practice, I guess.