Not upholding the first amendment; upholding the principle of the first amendment, that is, the first amendment doesn't create a right, it protects one that we all already have. The Bill of Rights are based on natural rights, ones we have by benefit of being alive, one of which is free speech. The First Amendment concerns itself with a very small corner of that universe, but the rest of it is ours, and should remain free.

The founders never imagined a situation where a very few private citizens would have the power to censor the speech of millions of others. Nothing even remotely similar to that existed at the time and there was nothing to suggest it could ever exist. The US Constitution is also a minimalist document so it wasn't concerned with enforcing behavior between private citizens.