In light of this the safest recourse is to simply not post anything online at all, for fear of being doxxed at some point in the future (an inevitability given modern standards for and cultural attitudes towards privacy) and subjected to invective for years' old posts and writings. This is the culmination and terminal state of "anonymous nonexistence" you refer to.
In this way the chilling effect achieves totality, and nobody feels comfortable sharing genuine thoughts online at all. It's arguable that this is a societally healthy state of affairs.