Skeptics and debunkers often take a reactive role. When something crops up that's got some bunk in it then they take some time to explain what the problem is, pointing out where the believers are in error. The amount of effort put in by the skeptical community is proportional to the amount of exposure a topic gets. High profile topics like 9/11, homeopathy, and UFOs get a lot of attention from skeptics, but low profile topics like chemtrails and FEMA coffins
get far less attention.
This is partly because the topics seem such obvious bunk. Chemtrails are just persistent contrails, and FEMA coffins are just stored grave liners. However the people who believe in these various theories seem to take them very seriously, and are going to quite considerable lengths to promote the theories.
Such topics are easy to dismiss when they exist outside of the mainstream, when nobody has heard of them. But if they make the leap out of obscurity, and suddenly acquire a mass of mainstream coverage, then they grab their claws into the minds of millions more people. And once those millions of people start to suspect a theory, it's very difficult to turn around.