TOR hidden services would be unreachable if nobody could run an entry node. Yes, services like GitHub would be affected just as badly as the likes of Facebook. Serious developers (like Microsoft and Google, and even those much smaller) can easily run their own servers though, so would the powers-that-be really care? Cloud computing may also be destroyed.

When I mentioned the DMCA safe harbor, I forgot that it only protects sites from copyright violations. Could a site like Facebook, in theory, be prosecuted for distributing terrorist propaganda when such incidents occur? Or in the case of other data-sharing crimes, like distributing child pornography?

Apparently, such issues aren't really settled. https://www.ericgoldman.org/writings/websiteliabilityalert.h...

Regulations don't have to be perfect to be effective.

It's easy to keep driving your car through an intersection without stopping at a stop sign, and some people get away with it.

Even though stop signs can be circumvented, we're all a lot safer with stop signs than without them.