Ah but if the landlords actually insist on their clientele behaviour in a certain manner (ie like civilised people and not drunken yobs) this shouldn't affect their current punters. Either the newcomers moderate or modify their behaviour or they get chucked out.

Joseph P is right. It's bloody hard work being a good publican and not everyone is suited to doing the job in the first place. Getting the beer and the environment right isn't even the half of it. How you handle your customers is the thing that really makes or breaks a pub.