Huh? FB could very well stop this and settle for less ‘efficient mass communication’ via many possible methods. Such as limiting the user base, restricting communication to friends of friends only, etc.
Obviously though a competitor with even less scruples will rise up and gobble up their marketshare if they did something that drastic. So the net result makes no difference.
To actually prevent child pornography from getting shared would require a dictatorship censoring the entire internet. Sure it would be the government instead of multiple big private companies, but that seems even worse than the current situation?
And if you go the other way and have millions of little networks, how do you plan on stopping all the bad stuff from being shared without an even more powerful and centralized dictatorship deciding who can form networks or not?
If you mean to get rid of all censorship and let free sharing of child pornography, etc., that will not pass any democratic legislature, at least in the West, since the vast majority of people want to limit that.
So in the end all alternatives would lead to even less freedom. Have you actually thought through any of this?