In the days since UnitedHealthcare CEO's shooting, the share price of parent company UnitedHealth Group fell more than 10%, along with the share prices of other major health insurers CVS Healthcare, Humana, and Cigna. On the other hand, UnitedHealth shares had roughly doubled over the prior five years alone. And there have long been complaints that insurers allegedly "wind up incredibly profitable at the expense of some patients," as one health-care equity analyst told CNBC.