I think it's pretty unfair for lesser players that don't have the great gear be singled out and kicked from an Ops group.
It's not "unfair" if they're doing it for an explicit reason, which "gear" is entirely appropriate to call someone out on. If you're trying to do content without sufficient gear, you're functionally asking that the people that *do* have better gear make up your own inadequacies. Just because you pay your $15/month (or threw a few dollars at the devs by buying some stuff from the cartel market) does not mean that you're instantly deserving of running with people doing a relevant piece of content, especially since the success of said content is based upon collective effort such that, if you're not doing enough, someone else has to make up for it. It's entirely appropriate within the purview of a group leader to deny someone a spot because they don't have good enough gear. It's not "Nazi crap", as you so eloquently put it; it's only bringing people that can actually carry their own weight.
Of course, to be described as being undergeared for SM Xeno, you pretty much have to be in unoptimized leveling gear, which is, honestly, laughably inexcusable, considering all of the free gear you get. If you're being denied a spot in an Hm group because of your gear, it's more appropriate because that requires at least full Columi to not get carried.
It also depends on what role you want to play: DPS can get along with marginally worse gear and sometimes healers, but tanks are almost never admitted if they're undergeared. If you're a tank, there are explicit times when you have to be able to take a certain amount of damage within a short period of time and no amount of healing is going to keep you alive. As such, if you're undergeared, chances are you're not getting admitted if the group leader knows what s/he's doing.
Even more so, there stands a pretty good chance that, if you're undergeared, you likely don't know the fight, and a lot of people just don't have the interest or patience to teach someone a piece of content (especially since, if you're undergeared, chances are better that you don't actually know how to play your class effectively and you'll need to be taught both your class *and* the fight/s in question to actually carry your weight).
Your entire argument is predicated upon you insisting to other people that you are entitled to run with a group doing a piece of content regardless of your actual ability to perform. That's not true. The only thing you're entitled to is playing your own character in whatever fashion you choose that doesn't break the EULA and Code of Conduct. Anything more than that is based upon the vagaries of the social contract, much of which, in operations, is predicated upon things such as gear, knowledge, skill, and personality in order to "deserve" a spot. If you don't like the fact that other players seem to exclude you, it's your own responsibility to address those relevant weaknesses rather than simply complaining that you're entitled to something that you're not getting.