For a good example of slippery slope in action wrt anti-semitic hate speech, look at how the BDS movement is attacked as both of these things.

Note: I don't support BDS. But I don't consider it to be either anti-Semitic nor hate speech, and the fact that many people who support hate speech legislation genuinely believe that BDS does qualify as hate speech, puts me firmly into the anti-hate-speech-laws camp. Simply put, I don't trust democratic majoritarianism to provide a definition of these things that I would consider acceptable, much less good.

Furthermore, given that hate crimes are directed towards minorities, and hate speech legislation is passed by majorities, I would posit that in any case where that speech actually makes a difference (i.e. where it can translate to tangible action), the majority will always immunize itself. Meanwhile, it will use such laws selectively against minorities (e.g. see all the right wing politicians referring to BLM as "hate group").