I agree athiests are the most distrusted minority, the reasons i think are many but a few i think compact the issue the most is:
ignorence - mostly from people who can't picture someone believing in no higher power of some sort, not that people are stupid (some are though)
but really people look at someone who doesn't believe in something higher as eather lying to themselves.
Thus the possiblity of being a lier and or corrupt or without a basis for morality, so that would make anyone who doesn't understand athiesism distrustful
another might be along the lines of limited pov, very much like the idea that a person without a religious compus is not really moral, people might do anything, immoral instead, it has a lot of emotion based things rather than rational based things
as we have seen many times alone on the board people have show the belief that no god = no morals or ethics = distrust because of the first idea