Bad AT! Bad!
Indeed the word "Crusade" is derived from "Crux" meaning "Cross" which is a symbol for Christianity. Like Hunpecked said, something along the lines of "Liberation" (or, in the case of aliens (or "Xenos") "Annihilation") would be better suited.
While reading 1984, it put me in a dark mood, but I was very happy to have read it. I can really recommend it.