Ethan Zuckerman is director of the Center for Civic Media at MIT and co-founder of the international blogging network, Global Voices . The opinions expressed in this commentary are his.

(CNN) The white nationalist leader Richard Spencer gave a speech Saturday night in Washington in which he invoked Nazi propaganda, questioned whether Jews were people and called America "a white country designed for ourselves and our posterity."

When he finished, the audience offered Nazi salutes and chanted, "Hail Trump! Hail the people! Hail victory!"

Spencer and others in the white nationalist movement see the election of Donald Trump and his appointment of Breitbart News publisher Steve Bannon as his chief strategist as clear evidence that their views are entering the mainstream.

The rebranding of "neo-Nazis" into the "alt-right" and the wave of media attention Spencer, Bannon and other extremists have received this year have lodged them firmly in the national debate.

This is a good thing.

Not because Spencer's blood-chilling racial hatred is good for political discourse in America -- it's not. But it's good news in the same way that Hillary Clinton's defeat in the Electoral College was good news for American progressives.

Had a few thousand voters in swing states stayed home, we would be celebrating the first female Commander in Chief and laughing about what a strange year 2016 was.

Instead, we're confronting the deep currents of racism, sexism, Islamophobia and xenophobia that infect American society. These currents have never been far below the surface in American political life, but have now come out to party. Had Clinton won, most of us still wouldn't know who Richard Spencer is.

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In the race to assign blame for Clinton's defeat and the media's failure to see it coming, pundits have proposed a host of possible causes: the Electoral College, voter suppression, unenthusiastic black voters, secret Trump supporters, third-party candidates, sophisticated ad targeting, fake news and the echo chamber of social media.

In 2013, I published a book that argued that while the Internet made it possible for us to hear opinions and perspectives from all over the world, the vast majority of us go online to learn about topics we're already interested in and to reinforce our existing biases and positions. Unlike my friend Eli Pariser, who places blame on unaccountable algorithms for "filter bubbles," I see these echo chambers as the result of the basic human drive toward homophily, the tendency of birds of a feather to flock together.

The Internet has allowed very different flocks to form than in analog days. In the days of three television networks, a relatively narrow range of political views were discussed in public fora. Journalist Daniel Hallin referred to three spheres of media discourse : consensus, legitimate controversy, and deviance.

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Ideas within the sphere of consensus weren't worth debating: democracy is the best form of governance, capitalism superior to communism, crime deserving of punishment. Media focused within the sphere of legitimate controversy: abortion in the second trimester should be (il)legal; economic growth will increase if taxes are (raised/lowered). Deviant ideas -- property is theft, white people are superior to people of color -- were not discussed for the simple reason that they didn't need to be.

Journalism professor Jay Rosen points out that if your ideas are within the sphere of deviance, you will always perceive media as being biased against you. Prior to the Internet, a white nationalist would have had a lonely existence, his views unrepresented by the media, unable to find anyone to agree or debate with. As sites like Stormfront came online in 1996, white nationalists found each other and a strange thing happened: They developed their own spheres of consensus, controversy and deviance, where ideas that were deviant in mainstream discourse became the common ground to build on.

"White supremacists hope that Steve Bannon's ascendancy expands the sphere of legitimate discourse to include ethno-nationalism and religious and racial tests for civil rights." Ethan Zuckerman

Trump's rise as a political figure has shown a deep understanding of Hallin's spheres. He repeated an idea that was deviant -- the elected president of the United States was a secret Kenyan Muslim -- so loudly and relentlessly that it became part of the sphere of legitimate controversy.

Mainstream news outlets (including this one) dedicated thousands of hours to debating a "controversy" that never should have been controversial. When reporters and pundits remind us that a Trump statement or action "is not normal," they're often signaling that Trump is bringing ideas out of the sphere of deviance and into legitimate controversy.

Shifting the borders of Hallin's spheres is a tried and true strategy for winning contentious political battles.

For example, America's expensive and convoluted system of private, for-profit health insurance might fare poorly against single-payer, state-subsidized healthcare in a robust public debate. So insurers have worked hard to ensure that "socialized medicine" stays firmly in the realm of deviance and that legitimate controversy focuses on whether or not we repeal the Affordable Care Act, which still keeps private insurers central to the American system. So long as we don't debate single-payer healthcare, it never becomes a serious threat to the existing system.

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White supremacists hope that Steve Bannon's ascendancy expands the sphere of legitimate discourse to include ethno-nationalism and religious and racial tests for civil rights. Progressives and others hope that the disgusting image of Nazi salutes at a US political rally will banish Richard Spencer and his ilk to the darkest corner of the sphere of deviance.

My deep fear is that there's no single set of Hallin's spheres anymore. What's consensus to a Trump supporter may be deviant to a Clinton supporter and vice versa. We now face an online media landscape so diverse and fragmented that each of us finds big enough spheres of legitimate controversy that we think we're seeing a real debate at work.

The danger is that there is no national dialogue because there's no agreement about what's legitimately controversial and worth debating.

When Spencer's followers make national news with their rendition of "Heil to the Chief," we can, and should be, terrified. But we should also be grateful for the glimpse into white supremacy's dark and paranoid world. We can, and should, consign their twisted views to the dustbin of history. We must ensure that America's promise as a nation of immigrants is not hijacked by racist ideologues.

But we also must take seriously the problem their visibility raises: How do we dissent and disagree democratically when we no longer know what's worth debating? If we can't agree that Richard Spencer and Steve Bannon are beyond the pale, what can we agree on?