Ah supremacists...Especially religious ones, are just scared. They're so scared of the unknown (death, creation, etc) that they cling on to whatever explanation the preacher can give them. After a while, they turn into this zealot that wants to spread the gospel....Why? I have no idea. I theorize that it may be that they're scared these "outside influences" will corrupt them. Either that or they believe all should follow their way because if people aren't following that religion, it makes it feel like the religion is null and void (Which scares the jesus out of religious fanatics).
Whereas some people might get angry when those zealots damn others in the name of God, Jesus, Allah, or whoever, I feel so sorry for them. They're just scared little turtles that like the shell more than the world.