Simple. The saying goes: “The enemy of my enemy is my friend.”
The liberal/left/communists and the Muslim extremists both hate Western democracies (especially the U.S.) and want them destroyed.
The liberal/left/communists know the Muslims are treacherous but believe they can control them afterward.
The Muslim extremists know the liberal/left/communists are unclean infidels and will begin killing them as soon as they gain enough power to do so.
Those in the West who understand the viperous nature of both, know they will only be free of the danger they pose when each group is permanently “dealt with.”
“The liberal/left/communists and the Muslim extremists both hate Western democracies (especially the U.S.) and want them destroyed.”
True, however some may argue, “But the U.S. is a Republic.”