Not that turn hard to turn off trust cabal and beat down a reaver.
Battle, sure, bards suck in the circle since limited mobility and no effective way to mitigate lag and DB. But in any other cabal, which I guess is really only the Tree, I'd laugh if one of my cabal mates came after me. Maybe a bearcharge enlarged giant ranger might pose a threat, but nobody else.
I may not be able to kill the reaver, but they sure won't be able to kill me unless I screw up royally. And after they try, you can make their life hell, since you can see chameleon and they can't (far as I know reavers don't get detect camo)
And what reaver is pissing off a harbinger bard for the sake of trying to get a PK?