You may be the head of HR, but even you have a boss. Second of all, i'm sure your company would rather apologize and correct your mistakes instead of spending money on what i'm sure a reasonable man would declare a witch hunt.

As for that letter, again, it came from a doctors office. It's the doctors statement about your policies. So one can gather from the letter that this particular physician happens to deal with this a lot. It's not the employee's fault that the doctor chose to express his distastes in that manner. If anything, your problem is with the doctor not the employee.

Now you are right that in a right to work state i would have little power, but you fail to recognize one thing. In your own statement in the next to last sentence "he's sowing seeds of discontent elsewhere....guaranteed". By your own words then you essentially have stated that it's really because you feel the employee is disloyal to your company. Which in most cases of unemployment is not enough reason for the employee not to get some form of benefits. You would then have to prove with credible witnesses that the employee willfully caused or created the situation in which he was fired, ergo consistent lack of performance.

This is a form letter from a doctors office. So you mean to tell me you would willfully fire an employee over something a medical professional said? Since that seems to be what you've said, then perhaps it is you who would be looking for a new job. If i were in that employee's position and you fired me over what a doctor has said; i'd go over your head to your boss/head of HR. Then i'd fill a wrongful termination lawsuit based upon what my state laws allow depending on the actions of your company. So tell me, is it worth the risk to your job security to fire me? The common sense answer is no because it would cost you far much more in the long run.