My god do I ever hate this fallacy. It's so common in part because we, as a mostly democratic society, consider ourselves equal to experts in everything. I'm not an expert in astrophysics, but when everyone who is has reached a consensus that the earth does indeed orbit the sun, I'll accept that idea is well-supported, has good reasoning and evidence, and explains a lot of things, even when they don't seem intuitive. If I have doubts, I can study and learn and really try to apply scientific reasoning to it, and not just jump to saying "well it seems unlikely, so I'll stick with good old fashioned geocentrism thank-you-very-much."

Unfortunately part of the problem comes from our media. We have journalists who are trained to talk about social or political issues, where there may be valid points on both sides. There's no factual conclusion about labor unions - some love 'em, some hate 'em. But giving these issues equal time is not the same as giving equal time to a doctor supporting vaccination and Jenny McCarthy. One knows what they are talking about and one is hurling hysterical guesses, and they are not equally valid as news. But when people see these issues televised or given so much notice, it emboldens anyone with a crackpot hypothesis to step up because hey, they're just as valid as the people with thousands of hours of education, experience, and peer-review, right?