The slippery-slope argument here is based on the fantasy that if you simply draw the right line, you will never have to revisit it. The fact is that we are constantly renegotiating the boundaries of speech based on values, norms, and threats of persecution. The problem is that renegotiating those boundaries is exhausting, expensive, and makes everyone mad, which is why most people prefer to shout “slippery slope!” and then never think about it again.