How come health insurance companies are allowed to discriminate against people with disabilities?

How is it legal for health insurance companies to discriminate against people with disabilities (I mean, medical disabilities), but other companies are not allowed to, like grocery stores are not allowed to? Or maybe it IS legal for other businesses to discriminate against people I am really just curious, that's all. About the legal process. Health insurance companies kind of make me mad, because of this issue. I know I am expressing a political opinion, but I ask you not to troll. If you have a different opinnion thatn me, you can argue for it, but please don't start trollin.'