I don't know the church's official position on it, if they even have one, but a lot of people view the sport as brutal and dangerous. That can't really be debated since the ultimate goal is to knock the other guy out. Sure, there is strategy and finesse in the sport and a fighter can win without a knockout, but that's not what most fans want to see. They want to see someone knocked out cold, something that usually involves a blow to the head with, in professional fights, no head gear on.