I was the NCOIC for "Project 100" (somehwere :-) -- USMC) started immediately following the Paris Accords in 1973.
Medical discharge, hardship discharge, and forced early out discharges, etc., etc., all fell under the umbrella of "General Discharge" under Honorable Conditions. (Memory is shot, but this is how I remember it and I'm sure I'll be corrected if wrong)
General discharge was/is also open for reassessment following a prescribed number of years later through petition to a Naval review board for conversion to "Honorable".
With that said, sKerry could have parlayed his Purple Hearts into a self requested Medical Discharge and recieved it without a hitch, but only AFTER 1973.
It would be very interesting to see sKerry's first discharge certificate! (That would be dated 6 years following his enlistment, back then)
This is what I remember as well. I recall that the General Discharge (the term "Convenience of the Government" was also used) was an Administrative Discharge - as opposed to one that could be meted out by a Courts Martial. Folks who couldn't hack boot camp were given these discharges, but were told that they could appeal the discharge after X years and get it upgraded.
This is the only scenario I can envision as some like a Bad Conduct Discharge or Dishonorable Discharge would, like a Felony conviction, prevent someone from voting, owning weapons, etc.