Facebook is not a 'communications infrastructure', is not a 'public square' and they have no obligation to do anything other than act lawfully, and then, to act roughly consistent with their own guidelines, which is what they are doing.
The comparison to 'Ma Bell' is irrelevant.
'Verizon or AT&T' - the actual modern incarnations of 'Ma Bell' are not intervening here, nor will they.
If you want to make up stories about people raping children in basements, then yo can do that on your own website.
" for how long will people tolerate an increasingly unreliable communications infrastructure?"
This question is upside down.
The real question is 'How long will most people tolerate a social network full of stupidity, make up stuff, fake news, and other garbage'?
QAnon is not the reason people use FB, it's the reason they leave.