I've been reading a couple of tumblr's on the FTM tag in regards to a couple of trans* service members. One of them got outed accidentally by a buddy. Even if you are trying to go stealth, and not let anyone know you are trans*, sometimes you just get outed by bad circumstances, and ill informed folks.
Hell, just the other day, a classmate in my management class just asked me outright if testosterone shots hurt. So even well meaning allies will sometimes not understand, and out you.
So to my mind, "don't tell" doesn't work so well when others will tell.