- discourage brigading

- discourage mob behavior

- prevent particularly biased individuals from skewing every discussion

- adds stochastic variety to the biases of the group

I don't see how approximate popularity is better than popularity for the first three factors. It would achieve the 4th in individual threads, but amplifying randomly-selected niche viewpoints in different threads adds up to the same biases across threads (unless the selection of blessed users is thread-independent, in which case the community has a randomly-selected group of first-class citizens).