As others have said, it’s ridiculous. As a kid, I also, carefully dipped the jewels into the hot water. You get used to it.
I don’t get that either. My feet are always much more sensible to warmth that any other part of the body, so if they get in, no issue. The balls are also, from what I daily perceive — but don’t ask me how —, the hottest part of the body, so they should be some of the least sensible to the warm water, which I can attest for daily.
All this debate sounds stretched.
I take a showering/bath here. I plug the bath, shower and then bath in the filthy water, then shower again to clean it. That makes me an hypocrit with an ecological conscience, I guess.