First of all I don't think BC is scum. He pushed the JeeJee lynch and was part of the town circle. Also he has appeared town in the conversations I've had with him. That said, I think he was/is wrong on syllo being mafia (not sure if you still think this?).
Second of all we have to prepare for a potential lylo. That means getting rid of people we don't have a read on. And while I agree Kenpachi is a lurker who can be hard to read, Sevryn has simply been lurking more hardcore this game. On top of that sevryn sheeped after BC on to Drazerk day one like chaos13 and JeeJee - in fact he didn't even comment on the varp case at all.