I find it unnecessary. if that is how someone feels, they can simply turn down people they don't want to play with (without giving a reason).
I would not say i find it offensive, but it does tend to make me cock an eyebrow at the person/couple. We all have preferences, but, sometimes expressing them is unnecessary. To be honest, my experience has been that when someone posts that, they do not just have a simple 'eh, they dont do it for me' preference, but genuine racism going on, to at least some degree.