I won’t buy that overpriced yuppie crap but at least I have the decency to stay out of their stores and not use their facilities, making room for the fools who do.
If I need to use a restroom, I usually try to buy something, even a pack of gum. But as I get older...when the bladder comes-a-knocking...I am not beyond going in and making a beeline to the head. And then I even buy something on the way out.
But I have no problem with any place specifying that you don’t occupy space unless you are a customer. And while it is true there are some places that would have no issue with non-customers milling around, I have seen from personal experience there are some places that have to actively discourage it because the courtesy is abused by people...especially in busy places.