I think that what they're doing is wrong. Denying access to people they know to be rowdy is one thing, but putting a blanket ban on a given race is another. It's just flat out racist. They're denying rights to entire racial groups so that others can "enjoy a pint in peace". Think about it, some arab or islander guy decides to go to get a beer at the pub after a long days work and they get turned away simply because of their facial features. Where's the justice in that??
To those who say 'what's the big deal? they can just go to a different pub': I don't think that we should be so tolerant (of racism). I realise that it's in the city, but suppose that it happened at the only pub within walking distance from their house, or if a large number of pubs started doing it. The justification 'it's not that bad - they can just go somewhere else' fails as soon as such racist practises become more accepted and more pubs get away with it, because what happens when they try another pub? They get turned away again, highlighting the problem with using such a reply to condone the pub's policies. Of course, I understand that a single occurence doesn't have much net effect, but to be permissive of such racism allows an attitude to develop which leads to a form of racism which is far more widespread and damaging.
