I'm curious. Is teaching one of the very few jobs that provide sick days as a benefit? In the states most salaried jobs include some type of paid, unscheduled time off. Any union job, whether hourly or salary also has this benefit. Except for very small companies, I doubt if any have a proof of illness requirement. Without that requirement, any complaint about teachers taking sick days, which they are legally entitled to under their contract, I repeat, irrelevant.
What level of illness qualifies as "sick enough"? If you've ever worked a job with paid sick days, have you ever used one when you probably could have worked? I know people who are useless with a simple allergy attack or headache. I know other's who go to work when they should be hospitalized. Even knew one who died on the job because he was tired of all the complaints about his "sick" days.
Like it or not, agree with it or not, the teachers are within their rights. Whether or not they are acting morally is something I'm not qualified to determine. Here's a test to help decide if you are qualified to judge the morality of their actions:
Sit down with your family, friends or co-workers and discuss this issue. But preface it with the information that you are a member of TERB and why you are a member of TERB. The truth, not the lame "I read it for the articles" excuse.