A part of the X-Men?
Throughout the movie we see that Colossus is continually harping on Deadpool to become a part of the X-Men.
Deadpool: [to Colossus]Listen! If I ever decide to become a crime-fighting shit swizzler, who rooms with a bunch of other little whiners at Neverland Mansion with some creepy, old, bald, Heaven's Gate-looking motherfucker... on that day, I'll send your shiny, happy ass a friend request!
From what we see, Deadpool is not really the embodiment of the X-Men, as he commits murder regularly, even if the people he kills are bad guys.
So what is the motivation for Colossus and I guess Professor Xavier to have Deadpool as an X-Men?
Preferable in-universe answers only, but out-of-universe answers are fine if necessary.