As they prepare to wrap up their current term, the nine justices of the Supreme Court hold in their hands the fate of one of the most important pieces of legislation passed in a generation, the Affordable Care Act (ACA).

If the court rules against the Obama administration, it will be effectively ruling against middle-class Americans and their health security. The Affordable Care Act would be expunged just at the moment, barely two years into its existence, that it’s beginning to make a powerful difference in the lives of millions of families.

Under the old healthcare system, many people passed on important immunizations and other preventive care services because they were too expensive. And often, failure to get that kind of care meant even more serious illnesses down the road. But thanks to the Affordable Care Act, 54 million Americans now have access to preventive care — like cancer or diabetes screenings — without the additional burden of copays or deductibles.

Twenty-six million Medicare recipients took advantage of preventive services free of charge in 2011. And 5.5 million seniors have saved an average of more than $600 each on pharmaceutical costs with the closing of the “doughnut hole” coverage gap written into the 2003 Medicare Part D prescription-drug bill.

Just as the Affordable Care Act is helping retirees who have put in a lifetime of hard work, it is also providing a hand to those just starting out in life. Two and a half million young adults have gained health coverage, thanks to the ACA provision that allows them to stay on their parents’ insurance plans until age 26. This benefit is especially critical during a period when the economy is slowly rebounding and many young people are still struggling to find jobs, not to mention employer-based health insurance.

There’s more — if you have a chronic health condition, it used to be that you could get cut off by your insurance company after it paid out a certain amount in benefits. But the ACA lifts these “lifetime limits” for 105 million Americans.

The new healthcare bill is good for companies as well as individuals. Small businesses, which have faced crippling healthcare costs, now qualify for several tax breaks that allow them to cover their employees without a big impact on their bottom line.

And there are more benefits to come, if the Supreme Court upholds the law and allows it to be fully implemented. By 2014, at long last, your insurance company will no longer be able to discriminate against you and refuse coverage because you have a pre-existing health condition.

The Affordable Care Act isn’t perfect. But its problem isn’t overreach — if anything, it didn’t go far enough. We should have included a public option that would dramatically reduce healthcare costs by providing competition to the insurance companies. The Congressional Budget Office has estimated that the public option would reduce federal spending by $88 billion between 2014 and 2021.

The public option was removed because of the belief that it might be too controversial, and that a more moderate bill would be less contentious and earn broad-based support. But of course, congressional Republicans and their allies were poised to mindlessly oppose any bill at all. Partisanship and obstructionism was their single-minded strategy all along.

There was going to be strife no matter what — we might as well have thrown the deep ball and passed the most comprehensive bill on the table.

So that brings us to this moment, in which Affordable Care Act opponents have engineered a court challenge to kill by judicial fiat the landmark reforms they couldn’t stop through the legislative process. It’s just a little bit ironic that the very same people who wail about “unelected, activist judges” who “legislate from the bench” are now turning to the Supreme Court for an outcome they couldn’t achieve in Congress. What’s motivating them is not constitutional purity, but knee-jerk opposition to any legislation that helps working families find some peace of mind.

The Affordable Care Act is saving lives and saving money for the American people. Its impact has just begun to be felt in households and communities nationwide. If it is overturned by the Supreme Court, important progress will be arrested and reversed. This is not a moment to revert to a healthcare system in crisis, where big special interests profit while skyrocketing premiums bankrupt families and small businesses. This is a moment not to destroy healthcare reform but to build on it — by adding a public option that covers even more people, provides competition and cuts costs further.

Woolsey, formerly co-chairwoman of the Congressional Progressive Caucus, has represented California’s 6th district since 1993.