How will they get those extra comments to be seen? They still have to log in and get past captchas and all the same issues that bots have always faced. Humans create a crushing volume of crap already and we already have ways to hide that from ourselves no matter the volume.
Imagine buying a bunch of twitter accounts that have already been active for 1-2 years and then making a bunch of Tweets to influence public opinion.
I've done some experiments with GPT-2 and it had so so performance refining with tweets. Using GPT-3 you could probably just do it using only generation.
