A ban certainly won't do any good. There are subtler ways of stopping vandalism than a banhammer, i.e. AbuseFilter. We don't need to martyr UHM like we did MarcusCicero, only to have to deal with his bullshit for months after our "ban."
I suspect we would have had to deal with Marcus's bullshit in any event, and the banning carried the added advantage that he could be burned and blocked on sight when he showed up, which nipped at least some controversy in the bud.