An important thing to note is that whether facebook has employees doing this or not, there's no shortage of services for hire that will do this for anyone.
Literally any social media site that's popular is guaranteed to have accounts whose influence is for sale.
While this is true, just for a second consider on which side the groupthink in these comments falls. The mentality that anyone who disagrees with you must be "brigading" or a paid shill is very dangerous. It's also a consistent sign of the lowest quality debate on both sides --- everyone thinks everyone else is a Soros/Mercer/Russian/Clinton shill or bot.
While I agree with your premise, I don’t think it applies in this case. It is good that people are more weary of what they read online. For one, the internet is rarely the source of truth. There are too many bad actors around. Second, if someone disagrees with a comment, they should reply to that comment with another well thought out comment. Downvoted and flagging require no effort and is an emotional reaction more than a logical argument. This can be gamed easily. Upvotes and downvotes are unhelpful in that herd mentality can easily game the system. Flagging people’s genuine comment is bad faith and has nothing to do with disagreement.
Literally any social media site that's popular is guaranteed to have accounts whose influence is for sale.