People who think Osama Bin Laden's death was a hoax are now being dubbed "deathers." A couple of years ago, the word "deather" referred to an entirely different conspiracy theory--the one about "death panels" in the Democratic health-care plan. That theory lives on in wingnuttia, but I guess we'll have to come up with a different name for it now. I suspect the new deatherism will prove more popular and last much longer.
In point of fact, conspiracy theories typically don't have names. For example, there's no official name for the JFK theories or the people who believe in them. They aren't called "JFKers" or "Kennedyers." Similarly, people who believe Obama is a secret Muslim aren't called "Muslimmers." These theories don't have names, yet they're as widespread as the ones that do.
But in recent years it seems there have to be specific terms for each type of crackpot, and the terms are created by adding -er to a noun associated with the particular theory. There are the truthers, then there are the birthers, then the tenthers, and now the deathers.
I think this practice started with the 9/11 doubters. They referred to their own movement as "9/11 Truth," the idea being that they were trying to get at the real truth behind the attacks. Since other people didn't want to credit it as being a "truth" movement, they began calling its adherents "truthers." By the time people began questioning Obama's birth certificate, the truther movement had been around for several years, and it was natural to dub the new conspiracists "birthers."
This way of using the suffix -er actually predates 9/11. Past examples include the terms flat-earther, young-earther, and John Bircher. It doesn't necessarily have to apply to kooks; it could be just a way of saying the person is wrong-headed. If you call someone a pro-lifer or a pro-choicer, chances are you are not one. My guess is that attaching -er to a noun has the effect of trivializing a cause that people within the cause take seriously, and it therefore carries negative connotations. There are exceptions, however. Star Trek fans have always called themselves Trekkers, while being derided by others as Trekkies.
According to dictionaries, the -er suffix is used primarily for comparatives like faster, where the stem is an adjective, and for agent-nouns like reader, where the stem is a verb. There is, however, a class of -er words derived from nouns to denote someone who has to do with something. This includes occupations (hatter), residents of a place or region (villager, Southerner, Icelander), and people associated with a particular characteristic or circumstance (old-timer, six-footer, lifer). I suspect this last usage is what the crackpot -er is based on.
One final observation is that this only seems to work when the noun stem has just one syllable, as in truth, birth, death, earth, Birch, choice, or life. When the subject of the conspiracy theory has more than one syllable, as in JFK or Muslim or Roswell, attaching -er to the word just doesn't sound right. We also don't do it if the noun stem could easily be misinterpreted as a verb. Presumably that's why the folks who doubt the moon landings haven't been called "mooners." And a good thing, too.