It's perfectly legitimate to charge less to someone who's less likely to make a claim, and more to someone who's more likely to make a claim. The "higher risk" person might not have an accident, and the "lower risk" person might have an accident. Say an accident costs $100, and there are two people insured. The company might gamble that only one will have an accident. So, they charge both people $50. But maybe one person never leaves home; they could charge him $40 and the other person - who drives a car with underinflated tires and has an auto accident every 2 years - $70. Both people still save money over paying for their own accident, and the company makes money either way.
The key here is that a company who can get a bunch of low-risk people in at a substantially lower rate than what those people would need to set aside, they will probably not have to pay out more than they took in. And that allows lower rates for low risks, which increases the number of low-risk people who may actually pay into the system without taking anything out. This is a self-feeding cycle. It doesn't take a genius to see that, with a large enough risk pool and reasonably accurate risk-assessment processes, everyone pays in less than they take out while the central organization still ends up making money.
But fine, if you, AC, think that saving $100 back every 6 months will provide me with the 250,000 I carry in coverage for someone else's medical costs for car insurance, you go right ahead and think that. Never mind the 100,000 I carry in coverage to me for uninsured motorist damage. Lemme know when you need a place to stay after someone who has state-minimum 25,000 coverage (if anything) hits you and makes you get physical therapy for a few months; I'm sure their insurance and the money you "set aside" will cover all your medical bills and personal car replacement just fine. Have fun putting aside money for your house insurance, too, since everyone is just fine putting aside more than the full amount of their mortgage (to pay for "stuff" too) into a savings account *while* paying off the mortgage and buying stuff.