If someone knew how to make not-shitty facebook, they'ed very quickly make tens of billions of dollars, achieve fame in the public sphere, respect in the technical sphere, and influence in the political sphere. Facebook would go the way of myspace and we would all rejoice.
The fact that, despite the immense incentive and numerous attempts, no one has ever succeeded at making not-shitty facebook strongly suggests it is an incredibly difficult thing to do. All the criticism in the world means nothing if no one can do better.
The network effect isn't an obstacle since you can be on multiple social networks. Tons of social networks have been successful since facebook. But all of them suffer from the same problems that facebook has.
The fact that, despite the immense incentive and numerous attempts, no one has ever succeeded at making not-shitty facebook strongly suggests it is an incredibly difficult thing to do. All the criticism in the world means nothing if no one can do better.