At a recent debate, Democrats Christine Quinn and Bill Thompson took turns extolling the New York that welcomed their respective immigrant grandparents 100 years ago. The candidates suggested they were running for mayor because the city no longer offered the same degree of opportunity and class mobility that it did in the early 20th century.

Think about that. They are nostalgic for a past that had barely escaped the notorious Five Points and Gangs of New York era. The good old days featured the vile slums chronicled by Jacob Riis in “How the Other Half Lives” and a political culture controlled by Boss Tweed and Tammany Hall thieves. Moreover, Quinn’s Irish ancestors and Thompson’s Caribbean ancestors likely were subjected to merciless bigotry.

And they want to turn back the clock to that New York. Really?

The incoherence of their “vision” would be shocking if it wasn’t routine. In a campaign season dominated by Anthony Weiner and Eliot Spitzer, Democrats up and down the ballot are in a demoralizing race to the bottom.

Beyond pandering to unions, party stalwarts seeking citywide offices often act like students in a high-school play. Faced with a pervasive lack of enthusiasm among voters, the candidates ratchet up their rhetoric with false passion, exaggerated claims and utopian schemes.

They’re not just promising a chicken in every pot. They’re promising new pots, new houses and child care and transportation — most of it free.

Thompson pledged a free lunch for every school student, regardless of family income. “We have a moral obligation to make sure our students aren’t going hungry,” he said, claiming that “the stigma” of free or cut-rate food kept families from applying. Inadvertently proving economist Milton Friedman’s point, the candidate put the cost of a “free lunch” at $20 million.

Quinn’s big idea was to promise better condoms, proving she’s suffering from Weiner overload. She told a Black Pride Heritage Awards audience there were too many complaints about the sizes and strength of the 37 million rubbers the city handed out in 2012. “We will be improving the NYC Condom,” she vowed.

Imagine what her grandparents would say about “free” condoms, which cost taxpayers $3.7 million last year.

On other topics — those pesky things that determine whether a city thrives or declines — the candidates are full of sound and fury, but not much in terms of ideas to better life in Gotham.

On crime, they promise only to handcuff the NYPD. To improve education, they’ll work more closely with the unions. On jobs, well, they’ll figure that out later.

Bill de Blasio, enjoying his turn at the top of the polls, portrays himself as the “most progressive” candidate because he pledges to raise taxes on families earning over $500,000.

He will “ask wealthy New Yorkers to pay a little bit more to guarantee universal pre-kindergarten and expand after-school programs,” suggesting the education budget of $24.8 billion is miserly.

For many New Yorkers, this is something of a golden age. But to hear the Dems talk, nothing works, everything is terrible and the whole civic order must be thrown over. Immediately.

Differences among them are insignificant. What they share is a belief that every problem, including imaginary ones, can be solved with a bigger, more powerful government. Even the NYPD, which they love to hate, would grow thanks to overseers and monitors.

All the promises of freebies are made in the name of the “middle class,” which is more a verbal tic than a genuine audience.

Real middle-class New Yorkers know that wasteful government can’t be fixed by adding more government. Middle-class businesses and homeowners are more likely to rage against City Hall’s ticket and fine blitzes, stupid rules and dopey bicycle lanes than to demand a handout.

They are smart enough to know there is no such thing as a free lunch, or condom, and that every government giveaway is attached to a tax, fine or fee down the line. They also know they’ll get stuck with the bill.

Which brings us back to Quinn’s and Thompson’s longing for their grandparents’ era. Let’s assume they are right — there was more opportunity then for strivers.

What changed? Lots of things, but most relevant is that government changed. It grew exponentially bigger, more expensive and more powerful. It taxes and regulates more, and it provides more people with more of life’s essentials and extras than ever before.

Could that be part of the problem? Could the size, cost and reach of government be stifling growth and upward mobility?

That’s worth a debate — and it really is free!

Denial is a river for O

That was some lecture President Obama gave on Egypt — if you like high-minded nothingness.

After delivering such platitudes as, “The Egyptian people deserve better,” he planted America squarely on the fence, declaring, “We don’t take sides with any particular party or political figure.”

It’s too late for that. Obama took sides when he rushed to help drive Hosni Mubarak from office in 2011. Egypt had no plan for what would happen next, and the last 30 months revealed the folly behind the idea that democracy springs from instant elections.

While the ultimate choice is Egypt’s, America could have helped midwife a peaceful transition to a broad, civilian government. Instead, as predicted here and elsewhere, the Muslim Brotherhood swept the hasty elections and moved toward Sharia law.

Even as opposition to the Brotherhood spread, Obama was silent. Our ambassador actually dismissed demonstrators and got too cozy with President Mohammed Morsi.

The military coup and the continuing bloodbaths now raise the specter of civil war. Such are the fruits of leading from behind.

Retirement fund’s unhappy returns

When Albany puts out news on Friday, you can bet it’s bad news. So it is with state Comptroller Tom DiNapoli’s report on the quarterly performance of the state retirement fund.

The return for the three months ending June 30th was a meager 0.29 percent. The Dow Jones stock index increased by 2.76 percent for the period, or nearly 10 times as much.

The $159 billion retirement fund, overseen by DiNapoli, is heavily diversified, but the tiny gain is not a small point. It translates into tax hikes because of the fund’s 7.5 percent annual guaranteed rate of return. When the return falls short, taxpayers make up the difference.

So Friday’s news is bad news.

High marks, low Marx

Here’s a bulletin from the dustbin of history: Vietnam’s Communist government is bribing students to take courses in Marxism, Leninism and the teachings of Ho Chi Minh.

“Students have been shunning such degrees because potential employers are not interested,” a college official tells The Associated Press. A student says the failed ideologies “are just not applicable to my daily life.”

Smart kids. Maybe American kids will wise up and burn the Che Guevara T-shirts.