The particular problem is said speech quite often leads to calls of violence. And when a few people get banned for that you get dog whistles, sentences that are encoded calls for violence. Eventually the new slang is recognized for being violent and then it looks like the site has allowed calls of violence for months.
A short version of this is, if you let a nazi come to your bar, you have a nazi bar.
Calls for violence are free speech. Calls for "imminent" violence that serve to coordinate it have been decided not to be.
When you claim that calls for violence are not freedom of speech, it's a slippery slope that leads you to absurdities like speech that could "lead" to calls of violence are not freedom of speech, or that secret codes that could be interpreted as speech that would lead to calls to violence are not freedom of speech, or that violent-sounding slang that is eventually recognized as being encoded speech that would lead to calls of violence isn't freedom of speech, or that people who own bars who host people who use violent-sounding slang that is related to secret codes for speech that could lead to calls for violence are nazis.
And since nazis deserve to be violently suppressed...
So which right do you believe in more, private property or freedom of speech?