Some of these theories are bizarre, some - hold water. Mix false and true for their own advantage is usual method of con artists from behind the scene. Another method is distracting public attention from real leads by BS. But nothing can be hidden forever and in some point, sometimes so unpredictable, the true show its face. Good when we have a chance to catch glimpse of it and show it to the world, now in our new media environment - virtual space of thought - it's become easy and handy.

Are they? Good question!

Who writes that you can totally trust? Most TV news is infotainment. Papers write what the editor wants.
It is easy to become paranoid about it, .....
eg If all evidence that could be related to the possibility of alien visits was laid out openly, most would accept that "they" have probably visited us.
As you suggest, aklimento, some hold water when you dig deep. The greatest weapon of the conspiracy theorist is the non-explanation of events. Or lack of transparency, if all else fails.

Thanks God we have Internet now. In blogs and comments, on forums vivid, vibrant word reigning. This collective intellect able to do miracles and I'm pretty sure we will see no one soon.