Of course, at some point an employer really has to consider whether an employee who is often away sick is contributing enough to justify his continued employmen

Of course, at some point an employer really has to consider whether an employee who is often away sick is contributing enough to justify his continued employment. That's not uncharitable — it's a fact: if one's not working, then one's not producing value, and if the value one produces is less than the cost of one's wages, then the employer is taking a loss. How many such losses can an employer survive?