The killing of United Healthcare CEO Brian Thompson is bringing patients' bitterness toward health insurers to the forefront.Stephen Maturen/Getty ImagesHealth insurers are coming under fire for increasingly denying patient claims for medical care.Investors are rushing to back startups using AI to automate the complex healthcare billing process.These 10 startups are helping patients, providers, and insurers improve health payments with AI.In the wake of the fatal shooting of UnitedHealthcare's CEO last week, public hostility toward health insurers has reached a boiling point.After Brian Thompson was shot and killed in Manhattan on December 4, social media exploded in morbid celebration.