Of course, there are conspiracy laws, sending people away to prison for decades. So there must in fact be actual conspiracies afoot somewhere.
But the problem I have with "government conspiracies" (secret UFO bases in the desert, reverse-engineered alien technology, covered-up lunar alien artifacts, massive prison camps being built for future incarceration of the populace, etc., etc.) is that this is the very same government that can't seem to manage to keep anything very secret for very long, can't seem to manage any long-term program without severely botching it up, can't fund any secret program without going 1000% over budget, etc. In short the government can't manage to conspire to do anything efficiently that we know of, so how can we trust them to orchestrate these mind-bogglingly complex conspiracies in secret?
Of course, to the true Conspiracy Theorist, lack of evidence of a conspiracy is proof positive that it exists, proof that the cover-up has succeeded.
Tin-foil hats, that's for amateurs. Steel wool inside a cap of metal screen door material, with a hem of copper foil - that's the ticket.