I don't know how Dissent does it. The only solution I can think of right now is to ask people to perform some time consuming human task before they can create a

I don't know how Dissent does it. The only solution I can think of right now is to ask people to perform some time consuming human task before they can create an account. That would limit the scalability of any sock puppet creator and at the same time it could serve as payment for the service if that task is useful.