The problem is: how do you tell who's a troll?
The fact this society exists is evidence enough that someone can hold something to be true that you find absurd, but still be genuine in their belief. You can point out one or two likely to be trolls, but you can't know for sure, and you'd just end up banning possibly one of the few sincere people here. Like JRowe: probably troll, but one of the fresher posters (in comparison to ckljamas etc).
I'd say yes to banning Truth Seeker, but that's nothing to do with how serious they are, it's to do with how every post they make is low-content, obnoxious, and just clutters up threads adding nothing.
Mind you, it's possible permabans are an admin-only ability: mods can just do temporary (if long-term) bans. In which case, the longest possible would suffice.