Agreed, that's kinda my point. The evolutionary theory behind why we have feelings of grossness is just that "this thing is potentially dangerous to me," so we developed this sense of "gross" so we'd avoid the potentially harmful thing (although a quick google search doesn't bring back the study i'm thinking of that demonstrated this). But obviously that reinforced/learned feeling might not always be accurate.

I get grossed out by plenty of things, so I have to consciously evaluate whether it's just gross, vs actually a problem. If it's just gross, I can consciously then decide to just get over it and have a nice swim (or whatever) regardless.

EDIT: Here's a couple links about what I'm trying to get at:

Study on disgust and the spread of disease: https://royalsocietypublishing.org/doi/full/10.1098/rstb.201...

Article on digust wrt the spread of disease: https://www.nytimes.com/2012/01/24/science/disgusts-evolutio...

I'm not sure about other cultures, but in Japan they're pretty explicit about washing before entering an onsen. They even discourage putting your towel in the water, wearing a bathing suit, or submerging your head (as well as going when you have open cuts or sores). But, they also prefer mineral water to chlorine and it's generally fed from a spring or the water is changed every day.

I'm not a fan of overly cleanliness, but not doing these things means you have to add more chlorine. In addition to the aesthetic unpleasantness of chlorine and other chemicals, it's harder on the pool equipment and like another commenter said, it should require better ventilation that most pools currently have.

This reminds me of being grossed out by particular foods. Nowadays I take the approach that if people have eaten it for a long time, it's probably worth at least a try.

Perhaps helped out because my #1 example is chicken. Who doesn't like chicken?... me, as a kid, because it was often prepared terribly.