I purposely picked a pharmacy because it's a more difficult discussion than, say, a sports equipment store. There's no easy answer. Ideally, for things that are life-and-death there would exist a government provider that anyone could go to. We should not be relying on the grace and invitation of corporations for life-and-death needs.

Blanket rules and arbitrary size limits won't work. If you have a blanket rule that companies can kick people out for any[1] reason, then you have your "only one pharmacy in town" problem. If you have a blanket rule that companies must serve everyone regardless of their speech/behavior, then you can't kick a disruptive customer out of your business. If you say life-or-death companies must serve everyone, then you get into the endless debate about what counts as a life-or-death company. We have to eat. Do grocery stores count? Restaurants? We spent 2020 agonizing over what counts as an Essential Business. If you say companies over a certain size (or monopolies) must serve everyone, then you have to set an arbitrary size and debate over whether company X is a monopoly. I don't know what the answer is.

1: Any reason besides discriminating against "protected classes" https://subscriptlaw.com/protected-classes/