I was watching the Fox News Channel the other day when the host asked a young, liberal man who supports President Obama how he could possibly think that other young men would want to buy a health insurance policy that included maternity care just because that kind of coverage was mandated under the so-called Affordable Care Act.  “Because,” came the instant reply, “they’ll also get ambulance service if they need to go to the hospital.”

This was a young man loyal to the president.  And loyalty, as we can see from his answer, can make a devotee say silly things.  Still, loyalty can be a noble trait.  But when it’s loyalty to someone you don’t actually know, when it’s loyalty to a politician you only worship from afar, when it’s loyalty to a president who cares more about his legacy than he does about you, then noble isn’t quite the right word.  Naive comes a lot closer.

Naive or not, this young, loyal, member of the millennial generation is precisely the kind of idealist Barack Obama desperately needs on his side if ObamaCare is to survive.  If millions of young people don’t sign up, the game is over.  Mr. Obama’s most important piece of legislation will die a slow, painful death. And no matter how many times he blames Republicans, it won’t matter.  His stature and his presidency will be in tatters.

But Mr. Obama’s team has always figured that young people will “do the right thing,” that they’ll sign up for the Affordable Care Act even if it isn’t quite as affordable as they thought.  Why?  Because they’re young idealists who are, well, idealistic, and care more about the welfare of the country than they care about themselves.  President Obama has counted on them to be “good, responsible people” who will sacrifice for the greater good.  Mr. Obama was betting the young and healthy would be willing to pay more for their insurance so old people more likely to get sick could pay less.  He was betting the millennials would do that even though the fine (or tax) was quite small if they chose not to sign up for ObamaCare. Such was his faith in their idealism, and their liberalism.  But mostly, such was his faith in himself — in his ability to sell ice cubes to Eskimos.

But there was another guest on another Fox show the other day who wasn’t buying what the president was selling.  This guest was angry because his insurance had just been cancelled and his premiums tripled from $100 a month to $300.  And what irked him the most was that with his new policy he had to pay for – ready for this?  — pediatric dental care.

It turns out this young man wasn’t married, had no kids and didn’t need or want pediatric dental care.  He seemed like a smart, decent guy.  But he didn’t feel any great need “to do the right thing” or be “responsible” just to make the president look good.

And he’s hardly alone. A new survey from the Harvard Institute of Politics finds that 56 percent of 18-to-29 year olds disapprove of ObamaCare. A majority believes it will increase costs.  And now, only 41 percent approve of the job the president (they once loved and admired) is doing.  Does any of this make you think these young Americans just can’t wait to sign up for more expensive insurance plans?

Last spring, before anyone knew what a disaster the ObamaCare rollout would be, a White House official said, “If there’s one thing we know how to do it’s reach young people.”  He had reason for optimism.  Young people were among Mr. Obama’s biggest supporters. But what Team Obama didn’t factor in is that even young, loyal idealists have their limits.  They’ll “do the right thing” until there’s a price to pay.  They’re in favor of raising taxes on the wealthy, until they start making money.  They’re in favor of affirmative action, until they’re the ones who don’t make the cut.  And they were in favor of President Obama and his ironically named Affordable Care Act until it wasn’t so affordable to them.  That’s when their loyalty morphed into another trait that has survived through the ages to ensure our well-being.  This one is called Looking Out for Number One.