a) They all serve a non-democratic and irrational agenda and usually advocate violence against the scapegoated group(s) - i.e. They are right- wing and mostly fascistic
b) They usually falsify information in order to prove their point. Alternatively or concurrently, there is a logical disconnect between those theoretically held responsible for the conspiracy and those the conspiracists choose as their scapegoat - targets (E.g. militia can make a case that the government is dictatorial, and go from there to attacking blacks).
mbs: These are associated factors, but not the crucial elements. It's the method of historical analysis that is at issue -- the imputation of inordinate power (including the power to coordinate and to keep secrets) to elites. Hence events that are artifacts of boring and indistinct social and cultural forces are imputed to little groups and plans. History as detective story. That is the tendency to which your posts are susceptible is Chip's point, I think. I should admit I have a weakness for this sort of stuff myself. I don't think you are a right-wing conspiracist. I do think some of your posts slide into reductionism of the sort alluded to above.
An additional point is the political uselessness of these stories, even when true. The stuff of constructive agitation is what people can readily see and feel, or think they can. Facts that are the object of endless speculation and counter-fact don't lead to mobilization, only to confusion and resignation.
mbs