I think it has something to do with tolerance. I think metal fans are more inclusive and tolerant whereas R&B/pop tends to attract more chavs and bad eggs than metal. I have only ever seen one chav metal fan in my life. Whilst I am sure most R&B/pop fans are tolerant, I think a greater proportion may be intolerant due to the chav dynamic. This means it is difficult to separate the good eggs from the bad eggs amongst more popular forms of music thus gay bars have to differentiate along sexuality grounds. I may be wrong though.

We need more metal pubs - Norway is full of them. And furs work in them too.