The majority of posters here are in the prime demographic to suicide
Did you mean that the posters are drawn from a demographic which has suicidal tendencies (young adults), or that Lesswrong is a demographic which has a higher proportion of people with suicidal tendencies?
Young males, often single, that is the demographic (though I believe that IQ is inversely correlated). Religion is a protective factor, and though singularitarian is not a recognized religion (though SIAI is tax exempt) its adherents hold beliefs that should have the same effect as those held by more orthodox believers.
I sometimes have thoughts of suicide. That does not mean I would ever come within a mile of committing the act of suicide. But my brain does simulate it; though I do try to always reduce such thoughts.
But what I have noticed is that 'suicide' is triggered in my mind whenever I think of some embarrassing event, real or imagined. Or an event in which I'm obviously a low-status actor. This leads me to think that suicide might be a high-status move, in the sense that its goal is to recover status after some event which caused a big drop in status. Consider the following instances when suicide is often considered: