...Government has decided that it is a bad decision for people to not purchase health insurance. I know many perfectly reasonable, rational people who did not purchase health insurance before the ACA because it was not worth it to them. I made the opposite decision; but there is no way that I could ever objectively come to the conclusion that their decision (or mine) was a good or bad one. Value is entirely subjective and for someone to impose their own subjective values onto another is asinine, coercive, and straight up maddening.
Except the value of insurance isn't subjective from the perspective of everyone else. If one of those "reasonable, rational people who did not purchase health insurance" gets hit by a bus and has the good luck to survive, then almost certainly it'll be everyone else paying for their treatment in one way or another. That's a direct 'objective' reason why having everyone be covered is beneficial, but there are other reasons why the requirement is there.
One such reason would be that removing the ability of insurance companies to discriminate based on pre-existing conditions pretty much compels something like it. Otherwise your perfectly reasonable, rational people would just wait until they got sick and buy insurance, and drop it as soon as they were better. That behavior would, of course, destroy the insurance market pretty quickly, which might be a bit of a problem.