In my opinion, in all societies (roughly) 10% of people on each end of the political spectrum would be considered to have extreme view-points; and 10% of those people (roughly 1% of the total) have very extreme view points which are frightening to most people. In no way should either group be confused for being "Typical" supporters for any major candidate for a political party because their views, values and beliefs rarely represent anything similar to the views, values and beliefs of their favourite candidate.
I could be wrong but I suspect that a large portion of these people end up being so extreme because they’re marginalized by society in some way or another, they become angry with certain elements, and they find kinship with these extremist organizations.
For every one of the extremist (potentially racist) hicks, there is someone who holds similarly misguided (and often funny) views on the other end of the political spectrum. My personal favourite (simply because it was ironic) was a group waving posters with phrases like "Homosexuals for Hezbollah" without realizing that members of Hezbollah would (typically) advocate stoning them to death because they were homosexuals.
