To take it a bit further, lets consider whether some forms of dementia are contagious.
This contemplation is offered in the sense that "a person is known by the company that person keeps", but more than that, I found sources which declare outright that dementia is contagious:
The latest research performed in Montreal at McGill University reported that if depression is not treated then it could lead to dementia or insanity. It means that your loved one can pass the disease to you.(Seniors, see also The Article Box). Which is another way of saying memes hang with like memes, and memes comprise sanity as well as insanity.
Canada has evidently become infected with the dirty energy meme in a magnitude that would make Exxon proud:
The people around the world who have considered Canada to be one of the beacons, one of the sources of environmental sanity, one of the places to always be a solid hope for the future of humanity, now fear that Canada has fallen into the abyss of human error.(Ecocosmology Blog). The oil barons of the U.S. going around religiously proclaiming "Oilah Akbar! Oilah Akbar!" while infecting millions, have now infected the Canadian government. Canada is now against Kyoto and Copenhagen.
The world has gone crazy several times before and can do so again if enough people fail to resist the memes of insanity.