The world is still a dangerous place. History shows that personal liberty has been circumscribed by society's ability to afford it. Today, however, society cannot afford not to have it. The military ban debate today bears a curious parallel to the debate over the draft and deferments during the Vietnam era. Selective Service is still alive and still can exert a subtle effect on other policy areas.
Gays can serve without harming unit cohesion.
Nevertheless, DADT is probably constitutional according to existing precedents. Homosexuality is indeed much more than sex. The gay community as we know it now very nearly went out of existence in the mid 1980's during the AIDS crisis. A workplace that provides opportunity likewise expects people to respect limits. The American people should decide how they want their Bill of Rights to read and should offer proposals to modernize it.