Sarah Perry summarizes and recommends John Stuart Mill's defense of free speech:

Perhaps more importantly, in a society in which dissenting views are rarely expressed, the prevailing views are often held as mere slogans or prejudices, with people rarely understanding the justifications or arguments for why the prevailing view is correct. In my introductory example, I ask why free speech is important. But if free speech is never challenged as a value, how can we be intellectually and emotionally aware of the foundations and reasons why free speech is good? Challenges to free speech (and other doctrines) are a gift, allowing us to reexamine why we believe in them in the first place.

Dissent, in this framework, should not be suppressed -- it is a valuable gift, allowing everyone to learn or revisit why they believe in the prevailing doctrine in the first place.

Perry links to "Abridging the Freedom of Speech" on The New Society Tumblr as an example challenge to free speech.

Speech can be used to destroy lives, to dehumanize people groups, and to influence others to cause harm. We acknowledge the dangers that certain forms of speech have. Therefore, it is only reasonable that speech that glorifies or otherwise supports standards that are not welcome in our contemporary community should be prohibited.

That's a hell of a "therefore". Which community would that be? Donald Trump has called for a ban on Muslim immigration and continues to be the front runner for the Republican Presidential candidate. The closing sentence really gives me the howling fantods.

The elimination of unsafe, undesirable thinking is a necessary step to establishing true justice in our time.

Set aside for a moment whether repealing the first amendment will actually help eliminate hateful thinking. How will a ban on hate speech be enforced in a country where a hateful clown like Trump stands a plausible chance at the Presidency? Eliminate the First Amendment and we'll be headed for The Handmaid's Tale, not some progressive utopia.