I understand the principle. I understand you have a belief. I share the principle, and used to have the belief. What I am asking you to do is test the belief on the basis of evidence. I am also asking you to do a cost-benefit evaluation of the principle in terms of other principles.
As you point out, free speech isn't absolute. There are many crimes of pure speech, from false advertising to inciting violence and soliciting murder. Society already has a complicated balance between principles like "free speech is good" and "people shouldn't be murdered".
There is also conflict here between "free speech is good" and "ethnic cleansing is bad". America has a long history of ethnic violence and ethnic cleansing (see, e.g., the Trail of Tears, or the Tulsa Race Riot, where white Americans carried out a ground and air assault on a prosperous black district, killing 100-300 and terrorizing thousands). As we saw in Pittsburgh, that era is not over. Reasonable people have concluded that a) Gab aided Bowers in his path to radicalization, and b) they do not personally want to support that.
Now you could argue that you are ok with some level of ethnic violence as a cost of free speech. You could even argue that unfettered communication is so important that we should diminish the freedom of association of people and their companies, requiring them to host Nazi. But if you are going to argue that, you have to argue that. Talking about warm and fuzzy principles is great, but if you aren't grappling with the costs, then at best it's useless. At worst, though, it's taken as a sign that you don't care about the body count. And it gets taken that way both by the marginalized groups supplying the bodies and by the people who are looking to create more corpses to further their principles.