The ACLU defended the Nazis in Skokie because they were denied permission to march on public streets. They were right to do so. But, contrary to a widely-held belief on HN, "popular" private property in the US is
not generally required to be available for protest, let alone for someone to set up their own shop peddling their messages.
Gab's complaint isn't that they're being "denied a platform" --- though that's one of several falsehoods they're surely like you to believe. It's that they're being denied access to the most convenient and cost-effective platforms. Essentially, they're demanding FRAND access to cloud providers for white supremacist Twitter. And FRAND isn't the default anywhere in commerce, let alone for white supremacists.
Someone was always going to take Gab's money. Even Stormfront, which is simply Gab without the pretend rules about harassment, is still up and running. As well, it was always going to come out which providers are willing to take Gab's money, and we'll see what impact that has on them in the market, when other people exercise their freedom of speech and association and refuse to do business with those providers.