There are a few who have a political agenda. For example, science denial trolls are all over the Internet. Their aim is to create the illusion of a scientific controversy by creating a bogus public controversy. It serves to undermine the public's perception of the level of certainty about some scientific issues that are politically under attack.
There is a kind of cottage industry for doing this and it parallels the political trolling that takes place in forums like this. The deniers have learned that one can directly affect the public's opinion by constant exposure to any particular idea, right or wrong. So constant repetition is used to simply condition the publics point of view.
The amazing thing is that it can go viral very fast. For every dishonest instigator with an agenda there are thousands more who have picked up the subject matter and learned how to debate it simply as an ego trip.
The talking points are so well worked out that one can almost pick up a science denier kit on the Internet and practice up on trolling in forums, picking a fight, and spreading the talking points around. It works very well, because very few of the other participants are equipped to sort out the bogus debating tactics and the bogus science.
Whether they believe the troll's point of view or not, the ensuing vigorous debate adds to the other readers' feeling that there might be a scientific controversy after all.