Rick Perry has gotten a lot of heat for describing the Social Security system as "a Ponzi scheme," and he deserves it. The Texas governor owes a big apology to Charles Ponzi.

Sure, Ponzi fleeced investors, but they at least had a choice about participating. Social Security operates on a compulsory basis.

In other respects, though, Perry has a point. In a Ponzi scheme, new investors have to be continually recruited in order to provide fat returns to earlier investors. It works fine until you have so many investors to pay off that you can't find enough new ones to cover the cost.

Social Security is like that. It used to be a comfortable arrangement for all, because there were so many workers paying in and so few retirees getting checks. In 1950, there were 16 workers for every beneficiary. But today, there are about three workers. In 20 years, the ratio will be 2 to 1. A sweet deal has gone sour.

Social Security can be changed to make it more affordable, and it undoubtedly will be -- by raising the retirement age, changing the cost-of-living formula, lowering the initial level of benefits, means-testing and the like. With this approach, the program could get by in something close to its current form.

But that option has a big downside. Any change that reduces outlays makes the program a worse deal for those who have paid in. As Perry noted (accurately), "By 2037, retirees will only get roughly 76 cents back for every dollar that is put into Social Security unless reforms are implemented."

Younger workers could expect a bigger return if they were allowed to take their contributions and put them into a 401(k) or something similar.

That option may be politically implausible as well as logistically daunting. But Perry is onto something vital, and he shouldn't back down just because pundits say he's risking self-destruction.

After all, George W. Bush was repeatedly slammed by Al Gore during the 2000 campaign for proposing that workers be allowed to direct some of their payroll tax contributions to personal retirement accounts. He got elected anyway.

Former Massachusetts Gov. Mitt Romney has lately taken on the Gore role, charging that Perry is "reckless, wrong on Social Security."

During last week's Republican presidential debate, Romney insisted, "Our nominee has to be someone who isn't committed to abolishing Social Security but is committed to saving Social Security."

This exaggerates the gap between Perry and Romney. In his book "No Apology," Romney doesn't rule out allowing "today's workers to direct a portion of their Social Security tax to a private account."

Perry has been vague about how, exactly, he would reconcile the interests of the old and the young. And he retreated in his condemnation of the program, saying he wants to "fix Social Security and make it financially viable for generations to come."

But at least he's raising the right questions.

Is this issue so politically explosive that Perry has done himself serious harm? We don't think so. Americans are not full of naive illusions about Social Security. They grasp how unlikely it is that the program can continue without major reforms. And they may be prepared to contemplate what those might be.

This campaign could begin an adult conversation on this vital subject. Let's see if Romney wants to be an adult.