That's what real liberalism looks like and it's something we need to extend to the federal level.
Actually they can. In most jurisdictions that's not a protected class. Nightclubs are well-known for having dress codes with vague guidelines such as "no gang colors". Some fancy restaurants require men to wear jackets or women to wear dresses (this seems politically fraught to me). Some bars don't let you in if you're wearing shorts. And so on.
Generally a protected class is an unchangeable attribute.
Can you cite a relevant case?
You do understand what a protected class is, and why it exists, right?
Yep. Like "No shirt, no shoes, no service." Or a more elaborate dress code.
Which is a simple "Terms of Service" for said establishment.
Facebook has a lengthier one[0].
I hate to break it to you, but bars and restaurants and concert halls can't kick out anyone they want to. There are rules around access to semi-public places. For example they can't kick someone out just for wearing a MAGA hat, or for being black, or lots of other protected classes.