Economists often talk about "moral hazard," the idea that people's behavior changes in the presence of insurance. In finance, for instance, investors may take more risks if they know they will be bailed out, the subject of ongoing political controversy, while the most likely person to buy an alarm system is someone who got robbed.
When it comes to health insurance, the existence of moral hazard is a more matter-of-fact issue: When people get health insurance, they use more medical care, according to a recent randomized study on the impact of Medicaid.