I do see what you're saying and I agree with you somewhat. an employer does have the right to expect and enforce certain behaviors on the job - but not off it unless a criminal act is involved.
I see the health care cost argument but it's too dangerous in our particular culture. Today it's smokers, tomorrow it's pregnant women and guys who sleep around. Today it's a health care cost issue, tomorrow it's behaviors that contribute to mental health problems. Maybe like being a gun owner or a Christian. No thanks!
What would really tick this guy off is if the fired employees opened a competing company next door.
How about just auto drivers? Employers could just as easily forbid all auto driving. (just get a green employer) Car accidents kill far more.