As a hyperbolic example, I've created a support group called "the summary execution of people with the username chrisco255 group", you're free to block the group and ignore us, but all 255,000 of us are very angry people looking for vengeance...
By the way, threats to life, liberty, and property have always been illegal in this country. But no, I'm definitely not afraid or worried about some idle threats from basement dwelling neckbeards.
How much more important is it then, to protect free speech on the internet, when so much power and threats are wielded in far more subtle and insidious ways?