Earlier quoted context omitted.
This is as it should be IMO. When you position yourself to be a de-facto public square, you shouldn't get to selectively operate like a private club when it suits you.
Isn't this punishing Youtube for their own success at achieving a dominant market position? They didn't position themselves as the de-facto public square so much as became one due to lack of competition.
An attempt at practical antitrust regulation might mean, for example, that if a Walmart replaces every other business in your town through the sheer merit of its business model, that Walmart doesn't get to refuse to do business with you on the grounds that the manager hasn't liked you since high school. It might even mean that you reserve Constitutional rights like assembly/protest within the area that is functionally the public square, which is the private sidewalk in front of the Walmart.
I know which approach I would prefer.