From my days as a DJ in night clubs, back in the days when the dress code was 'smart casual', there were sound reasons behind the 'no trainers' rule. The usual rule then was, 'no jeans, no trainers' which included no tee-shirts as well. The dress code was an effort to ensure that people made an effort to dress up in nice clothes, which usualy reflected a better level of behaviour - scruffy clothes often meant less of willingness to behave to an acceptable standard. Yes, it may seem unfair to judge people by the way they dress, but if you set a level of dress acceptance, it's easier to encourage the particular section of the public you want to include in your club. I guess these days, modern clubs have relaxed nearly all dress rules, and those that don't still adhere to the premise that smarter clothes mean smarter people. I'm not saying I agree with the logic, I'm just stating that this is where the idea stems from. If like Mozzer you object to being told whant you can and can't wear, the option to avoid such premises is always open to you.