Meh. Just give the screen a wipe before using it; the previous person may have used their fingers unwashed since using the bathroom, or covered in sticky food, or have spent a while up their nose.

As for people walking around and using the toilets in bare feet (or socks) ... I think it's disgusting, but it's a problem for that person; it has no effect on me. I'll be in my washable/plastic Birkenstocks. Which are sandals - sorry Saladman!