Military service at that time was still regarded by some as a
patriotic duty, particularly so by those whose fathers served
honorably in WW II and Korea.

That was pretty standard thinking among the people I knew in high
school, and early in the war that sentiment was fairly strong. As the
war went on, the public began to wonder what we were accomplishing.
When people began to distrust what the government was reporting about
the war, the sentiment changed.

Some others regarded themselves as
too good to serve and deferments weren't hard to get: get married,
become a professional student or have a critical skill like
engineering.

I"m not so sure about those categories for deferment. The college
student deferment did exist - that was a 2S, but I'm not sure it
carried over if you went to graduate school. It did carry over for
those who went to medical school, a 2M deferment, since upon
graduation there was great demand for physicians in the military.
Anybody remember if you got a deferment if you were getting a PhD?
Being an engineer didn't get you a deferment. One of my fraternity
brothers graduated with a degree in chemical engineering, one of the
hot degrees at the time (circa 1970), and got drafted a short time
after graduation. He got lucky. One day in basic the instructor
asked if anybody knew any chemistry. One guy said he had it in high
school. Another guy had some chemistry in college. Jim said - I'm a
chemical engineer. That got him a job in the lab at a military
hospital somewhere. Not very close to his degree, but it kept him out
of harms way. I don't think being married got you a draft exemption.
Nobody I knew got that exemption, so I suspect that one didn't exist.
Anybody remember?

Some didn't serve because they were deemed by the
government as unfit to serve.

Another fraternity brother - a likeable 'character', and not
necessarily a peacenik - starved himself till he was skin and bones to
be underweight. He was a walking skeleton, but otherwise seemed
healthy. Poor devil had to give up beer. I don't believe he had to
serve, but I don't know if his weight kept him out.

RWL