The thing is, though, it typically takes two people to actually have any kind of discussion. Now, if the typical situation were anti-DRM folks just spamming up every thread despite everyone else trying to just ignore them then I'd be right with you condemning such behavior. However, what typically happens is someone mentions DRM with respect to some game (whether to ask what it is, state they're not planning to buy the game because of the DRM, or state which distribution method they will or won't buy the game from due to DRM), then someone else feels the need to respond, often to criticize the topic of DRM even being brought up, and from there the topic derailment takes off. Other times the initial post on DRM is followed by a multipost bitch-fest about how DRM shouldn't be being discussed, which actually does more to derail the topic than the initial post ever could have (you commented on this phenomenon yourself in the Torchlight thread).
Of course what it comes down to is most people simply aren't willing to let comments pass, and feel some kind of need to respond to anything that rubs them the wrong way, even if the discussion has already been had multiple times before and derails the topic. Naturally neither you, me, nor anyone else can do much to change this behavior in others, all that can be done is to recognize such behavior in ourselves and hold back on postings that we feel ultimately wouldn't be particularly worthwhile. If enough people do the same, then there won't be an issue anymore. And while we're at it we can also go ahead and wish for world peace (hey, if we're going to be doing wishful thinking we might as well be thinking big).