I agree very much in principle, but pragamatically (i.e. in the real world) this strikes me as utopian and impossible, at least until human nature changes.

Toilets are a scarce resource (economically speaking), and thus there must be some rationing method in place. If it's not monetary, it will be something else. In a perfect world there would be plentiful bathrooms and everyone would diligently clean up after themselves and take the trash out when full, so operating costs would be minimal (power and water bill and occassional maintenance). In the real world though, people don't do that, meaning you have to hire people to clean. Some people will also vandalize, which gets expensive in a hurry. Public (government-run) restrooms tend to be even worse because they aren't actively monitored, and for whatever reason people like to trash them.

It's a proposed alternative to having no option at all. Restrooms are too expensive to maintain and prone to misuse to justify maintaining free options, which is why public restrooms have become virtually non-existent in US cities, following the eradication of pay restrooms. It is a much more moral option than giving the public no option at all, other than to become a customer at a business in order to be granted access to the business's restrooms, which would typically be far more expensive.

In some places, like Phoenix, the situation is currently so bad that even paying customers cannot use the restroom in some smaller shops, due to the large homeless population. Having any option at all, whatever the cost, would be a far better alternative.

The idea that giving up all your privacy isn't worse than spending a dollar really highlights something

Should people be able to use the toilet in your home? I mean, it seem odd to deny someone access to your private property for a basic human function?

I know sometime who ran a gas station. They had to clean their toilet after every fifth customer on average. That's a real cost.

Explain what's evil, please.

Wait until you hear about the cost of food, shelter, and healthcare…