you just simply DIDN'T do that in 1941 Britain, it would be professional suicide, and he probably wouldn't have been allowed to fly again.
Common fan theory is that the original Jack Harkness was actually murdered for being gay, thanks to Captain Jack snogging him. So it's a Stable Time Loop/Predestination Paradox: Jack gets his name from a dead guy, goes back in time, causes the guy to be dead, thus providing him with his name. Nice job breaking it, hero.