you mention state actors but overlook the bogeyman in our own backyard, whether it be the CIA, FBI, or even PACs. Yes Political Action Committees have people whose job is to maintain their view. PACs do it through mailing lists that combine specific people to maintain control over what is presented. with regards to sites like reddit you have those assigned to post and the list to rally those to vote up particular posts and downvote others to even mass report.

I know that many want to blame the other guy but sometimes that other guy is someone we know and their intentions are no better