I don't know what the answer is, but I do know that we need to support courageous journalists like Larsson and Gabrielsson who risk their lives to expose the truth of these hate groups. We could start by refusing to call these terrorists Christians. Hate, violence and intolerance are not what the New Testament teaches. We should also support organized efforts such as those by the Southern Poverty Law Center, who, among many other good works maintain a nation-wide list of hate crimes and groups. But perhaps most importantly we should remember that we are all immigrants (unless your family has lived forever in the African rift valley). I suspect the only countries without racial tension are those that are racially homogeneous.
If you want to find out about particular group, such as the California Coalition for Immigration Reform or the American Family Association, look them up here. It's really appalling how many of these groups exist in the US and the extent of their vile emanations.