Limiting what post rate? If it's coming from a farm it could have the same distribution as real people. If you read the article, you'll see that it's not about spam. It's about astroturf, and not even the kind where you just get a people to repeat your talking points. There are more subtle ways of diverting attention toward a legitimate message you find favorable, or away from a message you'd rather have people forget. That's all much harder for an automated system to detect, and the karma-whoring part harder still.

Look at some of the other comments on this very thread. Not the top vote-getters, but the ones that must have gotten two or three upvotes apiece. Several of those could easily have been generated by an AI designed to rephrase an already-popular view, perhaps with a pop culture reference or two thrown in to make it seem more authentic. Voila, instant karma, which can then be used in the ways the original presentation suggested to influence who reads what.

It only seems easy until you spend five minutes thinking about it.