So, Joe's corner pharmacy should be allowed to kick someone out of their store who's protesting, acting unpleasant, wearing a KKK outfit, or other First Amendment protected activities, but Walgreens shouldn't be able to? Where do you draw the line?
Walgreen's and CVS as a consequence of their duopoly/monopoly position do not have the right to kick you out of their pharmacy and prevent you from getting the medication you need to sustain your life (possibly quite literally) because they don't like the racist slogan on your t-shirt.
If you don't agree with this, you don't agree with freedom of speech, and any further conversation is basically pointless. You don't get to kill people by proxy or make people homeless by proxy because your don't like what they say as long as you can proxy it out so it's not the government literally directly doing it. It's just as unethical as the government warrantlessly wiretapping all Americans by buying data from data brokers hoovered up by FaceGoog, rather than building said system itself directly to skirt the laws.
The Constitution was conceived at a time when the government was the most powerful entity. Modern multi-national megacorps are arguably more powerful, and should be reigned in with similar restrictions.
Since I've entertained your scenario, in your reply to me, I'd expect an acknowledgement that preventing someone access to medication required to sustain their life, due to their speech, is effectively equivalent to killing that person due to their speech. You cannot have "freedom of speech" in a society where you can legally kill people because of their speech.
There's a huge gap between "social consequences" and material life consequences, and this is why "muh consequences" is a disingenuous argument made by people who actually are opposed to freedom of speech, but don't have the balls to say it (ironically, because they have the right to do so, but are afraid of the consequences).
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/
Speech discrimination is just another form of discrimination, and whether you can compel an individual acting as a sole proprietor or a family business to do something is a different question than whether you can compel a multi-national megacorp to do something. I don't know that "20 employees" is the line to draw, but it should be obvious on its face that a small business and an MNC are not the same, and they operate in society under different reasonable standards.
If 4 companies owned 100% of the property and in a region (as Visa/Mastercard/Discover/Amex do in the credit card industry) and worked together to limit the rights of people they disagree with to protest, you'd have a better point. That's clearly not the case. When you kick someone out of a store, they have the ability to protest anywhere else, and those are very real alternatives. I can grant you that that still limits the protester's speech to a small degree, but the ability to easily protest in many other ways mitigates the harm of that limitation. By contrast, people that are locked out of payments platforms have no alternative.
Similarly, if Walgreen's and CVS had a total oligopoly on pharmacies and colluded to exclude people based on political views, that would be a strong argument to regulate them.
Similarly, I'm not "harmed" as a Stripe user when an OnlyFans model or someone whose politics Stripe's executives disagree with receiving payments through the same platform. If there is a higher objective economic cost, pass that on through fees and stop trying to force the moral views of a few tech executives on everyone in the country.