Well, let me slam my wife in front of your 6 yr old then. When you have children who could potentially see it, it matters. To me, as an adult, I couldn't care less as long they don't get any fluids on my belongings.
But that's just it ... if they had to pass a law to make them bring something to the park to keep them from leaving dingleberries on the benches, I'm pretty sure they don't care where they leave their ... err ... bodily fluids ... I have just as much right to use the park as they do and I don't want to have to Lysol some jerk off's jizz off the bench before I sit down.