Sure, but I don't think they would say just ANYTHING. They'll always have some kind of reasons and facts behind their 'theories.' The whole 9/11 conspiracy theories for example...at least they bring up facts that DO make the events of that day look suspicious. They aren't just blindly saying that the US government flew planes into our own buildings while providing no evidence to back it up.
So basically, what Jim said is a good summary. We'll never know the whole truth, because if conspiracy theorists were just flat-out telling ridiculous lies they wouldn't tell us. And if our government was telling us flat-out lies, they wouldn't tell us. Life, death, and taxes will continue.