"It is a fundamental principle here in America, the wealthiest nation on earth, no illness or accident should lead to any family's financial ruin," Obama said.
Obama said he knows much of the discussion surrounding the healthcare act has hinged on its political consequences, "who won and who lost. That misses the point. It was a victory for people all over this country whose lives will be more secure."
Obama said he recognizes the debate has been "divisive" and he respects opponents' concerns.
"I didn't do this because it was good politics," Obama said. "I did this because I believed it was good for the country. I did it because it was good for the American people. …
"When we look back … we'll be better off because we had the courage to pass this law and keep moving forward."
The president said more than 250 million Americans who have health insurance will keep it and the law will "make it more secure and more affordable."
"Insurance companies can no longer impose lifetime limits on the amount of care you receive," Obama said. "They can no longer discriminate against children with pre-existing conditions. They can no longer drop your coverage if you get sick. They can no longer jack up your premiums without reason."
Under the law, he said, the 30 million Americans who don't have health insurance will have "an array of quality, affordable private health insurance plans to choose from" starting in 2014.
Romney, in a statement in Washington following the ruling that upheld the law's individual mandate to purchase health insurance, called the law "bad policy" and "bad law."
"Our mission is clear: If we want to get rid of Obamacare, we're going to have replace President Obama," Romney said.
Romney said he agreed with the court's dissenting opinion, adding: "What the court did not do on its last day in session, I will do on my first day if elected president of the United States. And that is I will act to repeal Obamacare."
Romney said the court determined the healthcare reform law did not violate the constitution.
"It did not say it is good law or good policy," he said. "It was bad policy yesterday and it's bad policy today. It was bad law yesterday and bad law today."
Romney said the healthcare reform bill would impose $500 billion in new taxes on Americans and cut Medicare by $500 billion -- figures that are disputed by supporters of the law.
"It adds trillions to deficits and national debt … and pushes these obligations to coming generations," he said.
Romney also called the law a "job killer" that puts the "federal government between you and your doctor."
The former Massachusetts governor said as many as 20 million Americans would lose their current insurance because of the law.
Romney said "real reform" of the healthcare system would require ensuring those with pre-existing conditions don't lose their insurance and helping states assure every American has access to affordable healthcare.
"And something that Obamacare does not do that must be done in real reform is helping lower the cost of healthcare and health insurance. It's becoming prohibitively expensive," Romney said.