Militant members of groups like the Aryan Nations don't typically see action in the navy or air force. The marines and army are largely ground based, and as one member said in the article to the link Intangible provided, they perceive an impending race war to be similar to Iraq.

I don't think many people want them in Iraq, because they complicate things even worse than most PMCs. When it comes to homosexuality, there are plenty of openly homophobic people, but almost nobody openly advocates naziism. They're the American counterpart of Al Qaeda, sneaking in and causing unneeded trouble. They want in, but if we want to truly end terrorism and restore stability to Iraq, we can't promote infiltration within our own ranks.