There are a lot of insane theories out there, and the internet, with its propensity to act as a digital soapbox for any old lunatic, isn't helping.
A brief stroll through the crazier parts of Google will open you up to all kinds of wild theories about everything from the species of the royal family to the exact mind-control chemical that the government is putting in your drinking water.
However, amidst all of the noise, it's worth bearing in mind that some of the most well-accepted ideas in science started as mad hypotheses. Giordano Bruno was burnt at the stake for suggesting that the Earth goes around the sun and even Einstein was laughed out of a fair few offices in his time for his General Theory of Relativity.
That said, it should probably be stated that, when we say that these theories might (might) be true, it's in more of an innocent-until-proven-guilty kinda way.
There are a lot of long boring processes that go into proving a scientific theory and the plausibility of a lot of these theories probably rests on your daily recommended dose but, hey, if you take life too seriously then you miss the fun of the fair.