Legality of getting fired for being sick?

That's how my job is too and people get fired all of the time because of it but however there is nothing you can do about it unless you have some terminal illness that you have to stay out for all of the time like cancer or having surgery or something like that and which case you can file FMLA and not be fired at all but seriously like someone else said how often do you really get sick though? I think I had the flu like once in January and that was the first time I'd been sick in almost a year.