If you think about it, there is common ground between extreme right and left on some issues. Single-sex education, for example - VERY popular among womyn-with-a-y feminists and MRAs alike. So it's not too surprising that some people make that leap.
See horseshoe theory.
The neoconservatives were people who changed their radical socialist politics while retaining their extremism -- they simply changed its direction, turning it first against the Soviet Union, then against the Islamists. People who see the U.S. as having a mission to spread capitalism and democracy throughout the world, by military force if necessary, are as extremist as any unreconstructed Communist.