Ideally, you could get rid of every captcha and just have an open API for everything. Somebody wants to create lots of email addresses to send spam? Remove the incentive to send spam.
Somebody posts thousands of manipulative tweets? Maybe the "feed" model of social media is wrong. Don't assume every random account is equally important. Better just have a simple social network where you can connect with your friends. Or even better, design your society such that it's decisionmaking is more resilient and can't be gamed.
The really hard but worthwile problem is not in tech, it is how we evolve our society along with the tech.