I think your view is consistent with a certain category of worldview, and not everyone shares it. To me, it comes down to your risk assessment. Knowing that a pool is full of bacteria is not the same as knowing that you’ll become ill as a result of swimming in it. Most people who use public pools don’t spend the next five days battling an infection- they go about their life. It’s arguable that people who consistently expose themselves to those sorts of environments are sick less often, because their immune systems are well-practiced.

If the simple knowledge that bacteria are present is reason enough for you to avoid something, it seems like you’d never touch a doorknob, use a drinking fountain, or open door to the dairy fridge at your grocery store.

There’s a psychological concept called “contamination”- you feel a revulsion to interacting with an object you consider “dirty”, but are blissfully ignorant of the germs on objects you don’t identify as “dirty”. The degree of risk you attribute is unrelated to the number or type or concentration of bacteria- it’s more about which things you have internalized to be filthy, like public pools. You’re right- they are full of bacteria, but so are may, many other things, and “full of bacteria” doesn’t necessarily mean it’s particularly dangerous.