Free speech is never 100% free, there are laws against libel, fraud, conspiracy, copyright, trademark, which create crimes that consist only of speech, or civil liability. Courts and parliaments have rules of procedure so it's not, whoever's loudest wins. And then there are social norms.
Slippery slope arguments are a slippery slope to never doing anything to improve anything.
It's always a balance between letting 20% of hateful crazy troll Nazis hijack all rational conversation, on the one hand, and blocking unpopular opinions on the other hand. Even HN moderates a lot.
Same applies to all the rights enumerated in the US Constitution, you have freedom of religion to the extent it doesn't infringe on the other important rights and provisions of the Constitution. Polygamy is banned. If your religion says servitude of women or Black people is God's will, you don't get to practice it. 2nd Amendment however broadly interpreted doesn't let you build a nuclear weapon in your backyard.
Also true, a lot of people want to block legitimate speech they don't want to hear and should be resisted. The first step toward fascism is indeed people not caring about free speech and thinking their personal discomfort is the most important thing, starting with the most powerful. Protesters get arrested and kettled, Colin Kaepernick loses his contracts. You're not going to stop the powerful from trying. It's never 'cancel culture' when state legislatures cancel women, minorities, gay or trans people, it's only 'cancel culture' when those people call out the powerful.
We need free speech, but letting liars and extremists run the public square and destroy all decency isn't the answer either. You need to protect free speech by having reasonable rules and norms.
"Arbitrary power is most easily established on the ruins of liberty abused to licentiousness." - George Washington