If I may be pompous for a moment, my participation in the SDMB has led me to formulate a theory about message boards and similar conversational media, which is that when someone is in an environment in which the overhwleming majority disagrees with him, and a fringe of that majority disagrees with him in unreasonable, rude, blindly partisan ways; that person tends to conflate the two and start feeling that the overwhelming majority disagrees with him in unreasonable, rude, blindly partisan ways.
Yes, the SDMB is heavily unbalanced towards the political left, so most SDMBers disagree with, and are opposed to, Sarah Palin. People being people, that means that most SDMBers, even ones who are genuinely intellectually honest and well-meaning, are predisposed to believe bad things about her, as opposed to Obama. And people being people, there are a fringe of SDMBers (cough, Der Trihs, cough) who are not only predisposed to believe bad things about her, but will do so with no evidence at all, in rude ways, etc. But the vast majority of SDMB leftists are not without reason. Look at the original topic of this thread. So there was a rumor that Palin might get divorced. How many posters took the rumor as face value gospel truth? How many said something like “if this is true, …”? The overall reaction was “if it’s true, kinda serves her right, because we don’t like her, but it’s just a rumor at this point.”
As for the issue you seem to find most damning, which (I believe) is the Trig-is-Sarah’s-baby rumor, there’s an extraordinarily important point which you keep ignoring: Suppose, for a moment, that the rumor were true. What would that say about Sarah Palin? Something negative? On the contrary, I’d argue that while such a factoid (Sarah Palin’s son is actually her grandson!) is obviously weird and titillating, it would actually be an incredibly noble act, one that would involve huge amounts of sacrifice on her part to better the lives of both her daughter and her grandson. In fact, the most salacious part of the whole thing would be the fact that it would involve her teenage daughter getting pregnant. Which, ironically, actually happened anyhow.
So that rumor appeared, there was no reason to immediately dismiss it as implausible, so we discussed it for a while, tossed around some reasons why it might be true and might not, and it eventually died away. At no point was there a consensus among SDMB leftists that it was true. Nor were there lots of posts where Palin was mentioned in other contexts and people responded by bringing up the Trig issue. Nor, as far as I know, was the SDMB the flash point by which the rumor spread around the world.
Would SDMB leftists have condemned it if some major news organization had reported the rumor as fact, or even likely; or had been involved in actively spreading it? Or if some senator had introduced a bill, claiming it wasn’t aimed at anyone in particular, which would require all VP noms to provide birth certificates for all their children and grandchildren? I’d like to think so, but we’ll never know, because none of those things happened. Most likely, some would and some wouldn’t, because there are no monolithic Usual Suspects.
So, to sum up… bearing in mind that people are people and have foibles and aren’t totally objective at all times… what precisely was so ridiculous about how the SDMB reacted to that rumor and/or the divorce rumor?