Yeah, I got the impression that Before was more concerned with what he might be facing within the pub, rather than breaking rules. Throwing yourself into a confined space, breaking whatever supernatural enchantments there might be against using combat magic in said place, to face a formidable starborn wizard, a formidable White Court Vampire, and a man that clearly has knowledge of things, is pretty ballsy.
I suppose that his Thrice Asked attempt at bringing Harry out might have constituted a "peaaceful" attempt, which might have done something in regards to any magical protections around the place. Although the Outsiders are from Outside, and fundamentally different from reality, they are still adherent to the magical rules of reality (they couldn't just pass through Demonreach's defensive barrier, a Thrice Asked from Harry later made Before give up his name). If Mac had some ward that acted similar to Harry's old wards, that somehow reduced a being's magical umph if they tried attacking, then his asking might have been to appease that. Harry's magical attacks might not have been similarly restricted, as he was a patron defending himself.
All theoretical nonsense, of course, because we have no reason to believe that's the case. But it might explain why he bothered with the Thrice Asked.