Why are some people so easily sidetracked by dumb conspiracy theories instead of using common sense?

I have read just about every ridiculous conspiracy theory that the people in YA can dream up in here and why are some people so easily swayed to believe them is beyond me. Doesn't anyone use common sense any more? Cant people rationalize whats real and whats fiction anymore? (WTC conspiracy, Health care reform euthanizing the elderly conspiracy, birthers conspiracy), and so on.. Really... haven't we had enough real issues to deal with on the table already that we have to go out and dream up new ones? Its no wonder the rest of the world sees us as a bunch of dummies, you are all proving them right.. don't you think?