Unfortunately, the "classes" the government refuses to allow merchants to "freely associate" with, or not, extend beyond religion to people other than you and me. Specifically people who aren't you and me. The Civil Rights Act was added to many times since '65.
Not really. A public accommodation (like this bar) cannot discriminate on the basis of (among other things) race, gender or religion (many jurisdictions also proscribe discrimination on the basis of sexual orientation, but many still do not). A bar cannot refuse to serve you because you're white, or because you're male. That sort of discrimination isn't historically common, but it is theoretically possible.
The court's decision upholds the liberty of a bar owner to refuse service to anyone on any basis other than one of the "protected classifications". Political ideology isn't a protected classification, so the bar owner retains all of the liberty that conservatives demand.
BTW, if I'd been the lawyer for the guy with the MAGA hat, I wouldn't have argued the religion angle, which is ridiculous. But it is demonstrably true that Trump supporters are proportionately more likely to be white and male. So I would have argued discrimination on the basis of race and gender, citing the disproportionate impact on white males of the bar owner's refusal to serve Trump supporters.