You speak as if there is an objective definition of "threats of violence or obvious incitement to violence" but I've seen people argue that as no less subjective (and therefore no less a slippery slope) as defining hate speech.
Some people could interpret a sentence like: "I don't like the taste of curry" to be hate speech, since it targets the ethnic food of a difference race. (For the record, I love curry...)
So yes, banning "hate speech" that does not threaten violence is a slippery slope, because it is simply too open to interpretation.
If it can be argued that one can apply a test of reasonableness as to whether or not a statement constitutes a threat of violence, then it should be the case such a test can be applied to hate speech. There's a risk of abuse involved in both cases, yes, but there is always a risk where the interpretation of language for political ends is involved.
Here's why you're wrong about your approach: if everything is subjective and the answer to everything is repression, then the law is no longer valid, and the only possible outcome is civil war.
If you do not want bloody, horrific, monstrous civil war with giant swarths of the population who don't agree with you, then you should err on the side of being permissive of questionable speech.
As you've seen from the mass riots recently in the USA, a massive violent response is only a single sensationalist news story away.
We need to support and encourage free speech.
We already live in a world in which limits on speech exist, including the limit against threats of violence being discussed. We also already live in a world in which every law besides the laws of physics is subjective and open to interpretation.
If it is the case that subjective reality must render law invalid, then the law is and has always been invalid. Given that the law does not appear to be invalid, and civilization appears to remain intact, it cannot be stated as a certainty that the existence of laws themselves (restrictions) in a subjective reality must inevitably lead to anarchy.
Your error is the fallacy of the excluded middle, assuming the only possible paths to take here are towards unrestricted free speech or arbitrary repression.
>If you do not want bloody, horrific, monstrous civil war with giant swarths of the population who don't agree with you, then you should err on the side of being permissive of questionable speech.
Arguments of the type "x or blood will be on your hands" appear more extortionate than appealing to reason. I don't believe that Reddit banning these communities will lead to that outcome, and if you consider that a likely possibility, maybe you should reexamine your assumptions.
>As you've seen from the mass riots recently in the USA, a massive violent response is only a single sensationalist news story away.
There was a lot more behind that then a single sensationalist news story.