Do you want to sit on a chair or bench after a person with a bare ass has been sitting there? I don't! That's why, when my Pagan group has clothing-optional events, we tell those who are going clothing-optional to carry a towel with them to sit on.
Besides, it's been my experience that the people most likely to go clothing optional, shouldn't. I'm no prize, either, which is why I keep my clothes on at camping events.