The way this works is that you just have to define something to be a "necessity" in the public consciousness, because there's a prevailing intuition that it's illegitimate to be asked to pay for anything that fits that description. Medical bills are a necessity, so it's illegitimate to be asked to pay them. You have to go to college to get a good job, so it's illegitimate to be asked to pay for an education. You need a place to live, so high rents are also illegitimate. And so on.