If you're looking to diminish your faith in the future of humanity, a good place to start is always the left rail of Twitter's website, whose list of "trending topics" details the most popular inanities of the day. But in France, this December, the Justin Bieber hashtags dropped down the hit parade and a much more sinister one topped the charts. If you clicked #SiMonFilsEstGay ("If my son is gay"), which trended for days, you could see thousands upon thousands of violently homophobic messages – suggesting that young people who come out should be imprisoned, castrated, murdered … you name it.

And that was not the only hateful hashtag of the month. There was also #SiMaFilleRamèneUnNoir ("If my daughter brings a black man home"), which brought together juvenile humor and appalling racism. Earlier in the month came #UnBonJuif ("A good Jew"), whose violent antisemitism seemed to revolve around cooking jokes; and if that was too subtle for you, there was also #UnJuifMort ("A dead Jew").

This whole vile outpouring may just be par for the course in the wilds of social media. But in France, hateful statements like this are more than contemptible. They're illegal – and the government noticed.

"These statements are prohibited by law," wrote Najat Vallaud-Belkacem, the women's rights minister, in an op-ed this weekend. "And those who make them are not less punishable and less likely to appear in court because they appear online."

To an American ear that may sound chilling, but it sounds quite different on the other side of the Atlantic. Like every other country in the European Union, France has a law that criminalizes incitement to hatred based on race or religion. (Think of John Galliano, the fashion designer, who was convicted of "public insults based on origin, religious affiliation, race or ethnicity" after drunkenly ranting about his love for Hitler.)

Homophobic hate speech is also illegal in France and 11 other EU nations. So whether or not anyone is prosecuted, making the point that hateful tweets are illegal is not an extraordinary step.

But Vallaud-Belkacem – one of the most highly visible ministers in France, the closest thing the French government has to a media darling – went further that that. She doesn't just want to punish individual tweeters after the fact; she wants to reform the whole system by which Twitter operates:

"At a moment when the government is putting in place an action plan against violence and discrimination committed for reasons of sexual orientation or gender identity, I want … to call upon Twitter's sense of responsibility, so that it can contribute to the prevention and the avoidance of misbehavior like this. I want us to be able to work together, along with the most important associated agencies, to put in place alerts and security measures that will ensure that the unfortunate events that we have witnessed in recent weeks will not occur again."

To that end, writes Vallaud-Belkacem, she wants Twitter to take steps to help prosecute hate speech, in line with laws already on the books. So long as they all respect universal human rights, she argues, each country has the privilege to strike its own balance between "free expression and the protection of human dignity". And Twitter, an international corporation, has to abide by each country's practices, rather than impose one on all.

As the minister observes, Twitter already has the capability to "remove manifestly illegal tweets, or at least to make them inaccessible so that the harm they have already caused to gay people does not continue." And indeed, Twitter recently did this on the other side of the Rhine. In October, the company censored the account of a neo-Nazi group after the German police informed Twitter that the organization was outlawed. If you visit the group's account from an American IP address, all its repulsive content is still there – but in Germany, you'll see a gray box and a statement that its content is illegal in that country.

Scary stuff for an American. Here, we're taught from an early age to be absolutist in our defense of free speech. But increasingly, the first amendment of the US constitution is looking a lot like the second amendment: an American exception so broad and so holy that it prevents us even from thinking about how to prevent harm.

The EU, Canada, Australia, and almost every other mature democracy recognize that words can be a weapon. But we don't regulate weapons of any variety in this country, and our kneejerk response to even the slightest intimation of limits to speech is a Voltaire-style refusal even to consider them. A few years ago, the late Christopher Hitchens melodramatically shouted "Fire!" in none-too-crowded theater, to demonstrate that even those few exceptions Americans admit to freedom of expression can be done away with.

If only this were still the 18th century! We can't delude ourselves any longer that free speech is the privilege of pure citizens in some perfect Enlightenment salon, where all sides of an argument are heard and the most noble view will naturally rise to the top. Speech now takes place in a digital mixing chamber, in which the most outrageous messages are instantly amplified, with sometimes violent effects.

When an incitement to hatred, such as the pathetic "Innocence of Muslims" film of this past autumn, appears on our screens, our first reaction is not to make response films praising religious pluralism. It's to reproduce it, virally and endlessly.

We keep thinking that the solution to bad speech is more speech. But even in the widest and most robust network, common sense and liberal-democratic moderation are not going to win the day, and it's foolhardy to imagine that, say, homophobic tweets are best mitigated with gay-friendly ones.

Digital speech is new territory, and it calls for fresh thinking, not the mindless reapplication of centuries-out-of-date principles that equate a smartphone to a Gutenberg press. As Vallaud-Belkacem notes, homophobic violence – "verbal and otherwise" – is the No1 cause of suicide among French teenagers. In the face of an epidemic like that, free speech absolutism rings a little hollow, and keeping a hateful hashtag from popping up is not exactly the same as book-burning.

What we face are two different and equally important questions. First, should hate speech be prosecuted when it appears online? And second, should Twitter filter access to that speech if it's already been deemed illegal?

I'd answer the first question in the affirmative. The second question is much more hazardous, and I don't pretend it's easy to answer. There will always be a need to balance the right to free expression against the imperative to prevent harm; the only way to get the balance right is to think very hard about who we are and what we care about.

One thing, however, is clear: the responsibility for answering that question must fall on us, on democratic citizens, and not on a private corporation. Our laws do not have to catch up with their business models. Free speech and protecting the vulnerable are among the toughest questions any democracy has to face – which makes it all the more dismaying that otherwise liberal folks defend the rights of tech companies to behave however they please.

It's up to us, not them, to decide how we want to live in common. We mustn't buy into the damaging fiction that technology deprives us of the freedom to make those rules for ourselves.