(Kevin Lamarque/Reuters) (Kevin Lamarque/Reuters)

President Obama urged a group of young activists gathered at the White House on Wednesday not to give up on the push to expand health-care coverage, saying, “You know, it's never been easy for us to change how we do business in this country.”

Speaking at the White House Youth Summit about his landmark health law, the president said it was worth working to defend the controversial law even though the online enrollment system had experienced major problems and come under intense political attack.

"But I hope you haven't been discouraged by how hard it's been, because stuff that's worth it's always hard," he said, addressing the crowd in the South Court Auditorium. "The civil rights movement was hard. Getting women the right to vote, that was hard. Making sure that workers had the right to organize, that was hard."

The president also took aim at conservative groups who have aired ads criticizing the law and suggesting young people opt out of it.

"Now, think about that. That's a really bizarre way to spend your money, to try to convince people not to get health insurance, not to get free preventive care, not to make sure that they're able to survive an accident or an illness. If I had that much money I wouldn't be spending it that way."

"And some of these ad campaigns are backed by well-funded special interest groups," Obama continued. "I assume they've got great health care. And just remember, and remind your friends and your peers: Imagine what happens if you get sick. What happens with the massive bills? The people who are running those ads, they're not going to pay for your illness. You're going to pay for it or your family is going to pay for it."

He noted that while young people might not think they need health insurance right now, they might regret that decision later.

"Look, you know, I do remember what it's like being 27 or 28, and aside from the occasional basketball injury, you know, most of the time I kind of felt like I had nothing to worry about," he said. "Of course that's what most people think until they have something to worry about, but at that point, oftentimes it's too late."