Teens and senior citizens are the most dangerous drivers due to lack of experience and declining motor skills, hand eye coordination, etc., respectively. Plus, there are some drivers on the road without insurance. So all decent/low mileage drivers subsidize these groups, to an extent.

But you're right, it is unfair to characterize auto insurance as a tax. It's more akin to a mandatory expense that should be factored into the price of owning a car and operating it on shared roads along with people of all driving skill levels.