(1) That's not our debt. Our $16 trillion in debt and our $87 trillion in "unfunded liabilities" represent two very different ideas: real past promises and projected future promises. Real past promises are, well, very real. We have to pay back our debt. Failing to do it would be an illegal and disastrous default. Unfunded liabilities are future promises, and, since they're not as real, we can change them whenever we want without destroying ourselves. For example, raising the taxable income ceiling and slowing the growth of benefits could reduce the Social Security gap to zero tomorrow.
And that's if there is a Social Security "gap" to begin with. Technically, it's not legal for Social Security to have "unfunded liabilities" since it can only pay as many benefits as it receives in earmarked taxes. Both it and Medicare hospital insurance are prohibited from spending money they haven't collected from specific revenue dedicated to their programs (i.e.: payroll taxes). It is impossible for either to technically be "unfunded", since they cannot legally outspend their funding.
(2) 75-year projections are scarier than they are informative. Seventy-five-year projections always sound gargantuan because, well, they're calculated over three-quarters of a century, which is an awfully long time to count anything. But here's the flip side: In 75 years, our economy will be massive. Growing slowly at a 2% annual average, our GDP would be $66 trillion in today's dollars in 2087. That's an incomprehensibly big number, too. Once you run out any number over 75 years, the mind starts to boggle. That's good for scaring people with mind-boggling numbers, but it's not so good for informing. When Republicans say unfunded liabilities come out to $520,000 per U.S. household, they're taking a figure from 2087 and dividing it over a 2012 population to exaggerate. Scary, to be sure, but not very informative.
(3) Projections can change fast. An unfunded liability is a projection, and projections shift all the
time for two big reasons: (1) Circumstances change and (2) laws change. Let's take circumstances first: The shortfall in Medicare and Social Security is exquisitely sensitive to just about every demographic trend you can imagine, including longevity, immigration, income growth, and birth rates. Furthermore, it assumes that seven decades of innovation will do nothing to change the rate of health care inflation, which is a brave assumption. We know next to nothing about how medical inflation will change after this decade. The fact that actuaries pretend to know the future doesn't make them oracles. It just makes them dutiful actuaries.
Now, about our laws. Strictly speaking, the U.S. doesn't have an entitlement problem, or even a Medicare problem. Rather, we have a health care cost problem -- medical insurance and hospital costs and so on are getting expensive faster than our ability to pay for them. Medicare and Medicaid are part of this big expensive system. If we cut these programs without changing the system, we won't be "saving" money, so much as shifting costs to old folks, who will be forced to pay much more for their health care, or else see much worse coverage.