I think that sometimes we are put into situations where we have no choice. I have worked a few different jobs (and these are restaurants no less) where calling in was not just frowned upon, but you could lose your job over it. One might say "Well, some people abuse the policy" but I am not referring to those people, but to people that worked 4 and 5 doubles a week and never called in. At one place I worked when I was 18, I was told I had to bring a doctor's note, which was fine, but it was a Saturday and my insurance at the time did not cover Primecare (walk in clinic). When I informed my boss of this, she insisted that I be treated at the ER (for a bad head cold, I might add, not an emergency) and pay $75 dollars for a note. For a head cold. When I balked at this, I was told, do it or no job. The same boss later did this to a girl that ended up having strep throat. At the time though, the job was too important to lose and being a student, I didn't have many options.
Anyway, I digress. My point is that some people are in a situation that leaves them no choice, and they may not feel that they have the option to get out of that job before finding another one. In that case, it is the employer who is rude for putting all the workers in that situation, not the person who must come in, sick or not.