This comment, in my opinion, is worth a re-posting. The commenter, "Grebulocities", indirectly addresses one of the mysteries of our time: "Why do so many smart individuals back dumb ideas, concepts, and products?"
To expand on my point a bit, I didn't think you thought that paid shills were behind apocalypse believers and conspiracy theorists. What I mean to say is that a substantial portion, probably most, of the posts you have to deal with that look like comments by corporate or political shills are likely to actually be real, unpaid opinions by people who have been convinced by propaganda of one sort or another. I'm going to use an example from something I know well (I studied molecular biology as a grad student for a couple of years), but this sort of process is going on in a number of political and economic arguments.
Take, for instance, a molecular biologist who has never read your blog before and whose views are scientifically mainstream. Suppose the post s/he comments on somehow involves genetic engineering of crops. His or her response is likely to be indistinguishable from that of a comment by a paid shill for a large biotech company - it will be articulate, it will come from a new user, and it will likely start by dispelling common misconceptions it thinks "anti-GM" activists have and conclude by saying that a biotech-driven Second Green Revolution is the key to feeding humanity.
Of course, the reality is more complicated - genetic engineering has shown quite limited promise at engineering better food crops, and it is mostly used as a way for a few corporations to gain intellectual property rights over large parts of the world's food supply. The actual innovations, such as inserting glyphosate resistance or production of Bt toxin, are being easily defeated by evolution. Numerous glyphosate-resistant weeds and Bt-resistant corn borers have appeared all over the Midwest and are defeating efforts to combat them with biochemical tools.
Now of course molecular biologists should know what's really going on - anyone who understands evolution would know that the techniques that have been used are guaranteed to fail as resistance evolves. In reality, though, they often side wholeheartedly with biotech firms and would make a post like this, assuming anti-GM activists are scientifically illiterate.
Some of them receive corporate grants and are biased for obvious reasons. But - this is the important point - most such people are not receiving corporate grants. Their sense of purpose and meaning in life is built around improving humanity scientifically, and they imagine that further scientific progress in agriculture can solve future world food supply problems. This happens to be exactly the view biotech firms are pushing - so you'll never know if such a post is originated by a truly (financially) disinterested scientist or a paid spokesperson of Monsanto et al.
This same process occurs in political issues as well, or anywhere else where educated people have personally identified with exactly the beliefs that certain interests are pushing. The situation from last week where someone falsely appeared to be a paid shill of the Democratic Party or its allies is a classic example - I know many highly educated types who would have made exactly the same sorts of arguments. A person who believes in Progress, and who believes that the Democratic Party is advancing Progress, would make arguments that sound like (and are in some cases taken from) the Democratic platform or Obama's slogans. Successful propaganda propagates itself.