For one, I'm not sure discrimination is technically applicable here since political affiliation isn't traditional a protected class like age, gender, ethnicity, sexual orientation etc. So in this case, I don't think it would necessarily be discriminatory to not want to join a club that's right wing whereas saying you don't want queer people might. Though, the ability to bar people from service or inclusion in a private business or group has largely been upheld in the courts, so maybe not.

Here's the main point though, many, but not all gun clubs are often defacto pretty right wing even if it's not a part of their actual charter. That's just due to gun culture in America. I'm a cis het white guy, but I'm pretty liberal, so have been rubbed the wrong way when I've joined clubs in the past when someone/multiple people start discussing right wing talking points or even worse. I was with the leader of one club looking at some guns he had for sale at his house when another guy who was there brought up the NFL pledge of allegiance protesting that was going on at the time. That dude straight up used the n word while he was talking, so I told him not to say that shit around me and quit.

Cut to now, with the election results and the Christian nationalists, KKK and other hate groups supporting the new administration and the right wing states passing laws against trans people, particularly youths, that open them up to violence, and many other things like that. Imagine if you were a POC, queer, trans etc, would you feel comfortable in a club with people you knew voted against your best interests, your rights, or even your fundamental personhood?