Deadcalm - the point is that if you're not 100%, then you are a danger to your colleagues and the customers (pilots/pax whatever). There was one former colleague of mine who had a perfect sick record for many years, but who came to work while suffering from heavy colds, and the signs of flu, or so I suspected on more than one occasion. In that state, they could not have been fit for duty but he still worked, much to the dismay of his/her fellow ATCO's. That is the point I was generally making. I am not as doctor and have no medical training but that does not mean that people who come in with a 'condition' of some sort are categorically not spreading bad germs around their workplace.
I'd much rather the system grinds to a halt due to people being genuinely off sick than by someone who has an incident while at work when they should be off sick. We have had quite a few problems at Bristol this last year or so with sickness and at times it can be disheartening with all the shift changes from the norm to cover for it, but better that than having the sick in working when they shouldn't be!