I've seen some excellent responses here about communism and why it was/is feared by many Americans. Then again, there are a few in"duh"viduals here that apparently have not studied up on communism's effect on the 20th century. First, go read the communist manifesto by marx/engals (sp?). Its a good place to start as per what communism was supposed to be. It all looks good on paper, doesn't it? Then go look at the history of Russia after 1918. Communism in its practiced form has proven to be not only unsustainable as an economic system, but a system that severely restricts the freedoms and liberties that this nation was built upon. (see declaration of independence/constitution, writings of Thomas Paine, John Locke, etc for these) It is a brutal system that does not respect people as individuals, only as workers, which are expendable as evidenced by Stalin's purges.
It is not also just a matter of rich vs poor in terms of rejection of communism. The "lower classes" tend to reject communism in the west because of the things I mentioned above. If it were just a matter of economic class struggle (the rich being in control of this nation and therefore using propaganda to thwart a threat to their wealth and power), then why didn't we eventually fall to it as per the inevitability of worker's revolutions as stated by this "scientific socialsim" advocated by Marx? Take a good look at the Weimar republic as well. (germany, post ww1/pre nazi era) With the economic conditions there of hyperinflation, unemployment, etc that had never been seen even in the heart of the depression here, why didn't they fall to and embrace communism as a form of government to feed teh people? Furthermore, why were teh nazis able to use anti-communism as a major tool of their campaigns (political campaigns, not the military kind of which we are all familiar with. The nazis were a party that did have to compete with the spd, kpd, z, etc. in parlementiary style government before Hitler became chancellor)?
There are a lot of reasons why communism is unpalatable to the vast majority of Americans. It may take some research, but it is definitely an interesting subject. Communism (as practiced) and Capitalism/democracy are almost exact polar opposites.