Xenophobia

Xenophobia is an irrational, unreasoning fear of that which is foreign or alien to oneself.

Throughout history xenophobia led to like minded individuals banding together into groups such as Terra Prime on Earth, the Alliance for Global Unity on Bajor, and the Vulcan Isolationist Movement. Such groups often committed terrorist activities and other crimes. (,, and )

In the 23rd century severe xenophobia was considered grounds for dismissal from the Federation Starfleet.