They are saying that they don’t feel like their hands are getting dirty by touching their dick because their dick is in their underpants all day.

The flaw to this argument is that your dick and balls can get sweaty and gross in there. And when you touch it, your hands can get gross too. Not to mention that your hands can get gross just by walking around and touching things in society. And the bathroom stop is meant to be a bio-break that enforces washing all the germs from your hands from walking around in society.