In a general way, I would agree with you. However, my experience has been that topics such as Israel/Palestine, GM and 9/11 attract an unusual amount of attention from astroturfer types (by which I mean exceptionally opinionated people who have not logged into the site for months or years, and have never made a contribution to a technical discussion).

I look at a thread like this and consider you and your downvoters to be two sides of the same coin. You might feel the need to beat the drum about Monsanto and GMO. Others feel the need to beat the drum for pushing forward with the boundaries of knowledge and the benefits that it can provide. You're being downvoted by people who feel differently than you do. Dismissing them as trolls, astroturfers or noncontributors (you don't know who they are) seems to me like rationalizing or propagandizing.

You might be right, but I usually still don't care about it. Topics like that usually have a higher bar for thoughtful comments, but the ones that manage to get over that bar are still visible and discussed. Astroturfers are annoying, but then again karma is just random Internet points; what matters to me more is if a comment manages to start a discussion involving other HNers posting interesting insights.

Karma isn't just random Internet points (in fact, that purpose of karma is pretty irrelevant and one's global "karma score" could just as well be removed without consequence.) The real point of voting is that it sorts comments, so that the dross of a conversation can fall below a certain line and you can stop reading the conversation before that line. Astroturfers negate the value of sorting, such that you have to read (or at least skim) the dross if you want to find the good comments.

Well, I guess I don't trust greying-out that much or am just curious, but I tend to skim the heavily down-voted comments anyway. Every now and then, one can find a pearl of wisdom in them.