We should not just assume absolute freedom of speech is an unalloyed good. What are the benefits, and what are the consequences? Because in this case, the consequences are pretty clear.
Censorship is evil. It is a power that will be abused for political gains (as we're already seeing). That is pretty much a constant throughout human history. The internet itself was a platform for free speech. That's what made the internet of the 90s so great. Now look at it. A handful of mega corporations spying on everyone all day every day, and controlling what they're allowed to see and talk about.
It's all very 1984, and everyone seems asleep at the wheel.
And we already accept limits on free speech. For example, can I publicly lie about someone as "free speech"? No, it's libel/slander.
For example, if criticizing the government is banned, that's totalitarian. If saying "All members of group x should be tortured to death" is banned but criticizing the government is not (unless the government is torturing group x to death), then it's not totalitarian.
Do you intend to control the latter as well, in the name of your "community"?
Speech is never "just speech": it enables and compels people to take actions. That's why free speech is important in the first place. In the same spirit, that's why free speech doesn't mean freedom from consequences.
Speech can motivate, encourage, inspire, disgust, leave indifferent, irritate, and so on -- but people who act on a given idea do it of their own free will. What authoritarian government fears is that people use their independent minds, allow disagreement and debate, and choose to act in defense of their freedoms.
Gab is perfectly free to entertain whatever politics they like, unfortunately for them, the eco-system around them is also free to react by refusing service to them.
Maybe they'll need to switch to a listserv? Whatever the case, it is perfectly OK to deny Gab services, just as it would be OK to deny doing business with Facebook or Twitter.