Let the military decide.
The military doesn't decide. Its elected political master in the White House does. I have heard that the original rationale was to reduce the number of on-base suicides. We need to offset that against the danger of being attacked by deranged shooters. Should we abolish the Second Amendment because gun suicides exceed gun murders by a factor of 2? Endangering the normal to save the suicidal from themselves seems a little unfair.