I would neither encourage nor discourage to join the military--but I would certainly do my best to EDUCATE anyone close to me regarding conditions in the service, be they female, male, gay, straight, or an alien beaming in directly from Pluto.
However, education is the answer only insofar as ignorance is the problem. If you've got someone sincerely wanting your input, that's awesome (and a big responsibility), but if the person's mind is made up, who listens to good advice, anyway?
Case in point: My first wife's brother joined the Marines when he was 17. Both I (who had by that time completed my 2 years of draft-required Army service) and his father (who was not a veteran but was also nobody's fool) attempted to dissuade him. We knew his personality was not going to "cut it" in the military.
Which it did not. He did survive boot camp but was booted from the Corps after something like 6 months of time in service. His "mental block" was illustrated perfectly by one of his statements to his parents after he'd been in boot for a while:
"I can't believe they're actually teaching us how to KILL people!"