In general, conspiracy theorists should be neither dismissed out of hand (and various "fast way" arguments like "too many people would need to have been involved are just not valid) nor accepted unquestioningly. Rather like economists really.
[WS:] I am generally with you, except the above. I think conspiracy "theorists" should be out of hand dismissed as nutcases in the same way a rational person dismisses religion. One dismisses religion (or conspiracy theories) out of hand because its proponents have no way of knowing what they claim, even if some of these claims may turn consistent with scientific discoveries (even a stopped clock shows the right time twice a day.)
Conspiracy "theory" is NOT about the possibility of human involvement in the causal chain of events, just like religion is not about filling in gaps in scientific knowledge. Unlike rational/scientific mindset that "knows" what is empirically supported, the conspiracist or religious mindset "knows" what it "makes sense" to it and fulfill its need for emotional closure - regardless of contradicting evidence.
Wojtek