America's founders believed that freedom of speech, the ability to express political and religious opinions, even unpopular ones, is central to self-government. Of course, this freedom, like all freedoms, has limits, particularly when it comes to putting others in actual danger. We can't shout, "Fire!" for example, in a crowded theatre.
However, an emerging group of radicals on the left has embraced a new belief: that just about any ideas, other than theirs, are not only wrong, but dangerous. And so instead of arguing or debating, they've committed to shut down expression by, and I quote, "any means necessary."