Listen mate, you gotta give something to gain something.....
Liberty may have big ships but they cant just go about blowing people up. Xenos can.
You want to fight liberty in a GB, go talk to Rogues and LH's and see if you can fly for them.
For what Xenos are, you fly a fighter and you do your damage without any RP. So you give up your right to Fly anything bigger than a fighter. *Simple*