It feels like it might be one of the best ways to combat bots and spammers right, and also avoids the life impacting edge cases when a real person gets banned by whatever automated system with no hope of recourse.
It seems to have worked too. Originally free accounts were great for getting people to sign up on social media websites. Well now it seems like we are approaching saturation, and most people with internet have an account on the most popular social media sites. Probably a good time to go back to paid accounts again.