RUTHFULLY YOURS

It’s too bad every New Yorker who plans to vote in the city’s mayoral election Nov. 5 couldn’t be at the Brooklyn Bridge Tuesday morning. They would have seen the single most important issue in the race between Bill de Blasio and Joe Lhota. It’s not stop-and-frisk.

Thousands and thousands of charter-school parents with their young children—most looked to be in the first to fourth grades—marched across the Brooklyn Bridge to City Hall to save their schools.

When Bill de Blasio won the Democratic nomination for mayor, the first question many asked was whether Mr. de Blasio’s intention to heavily regulate the police department’s stop-and-frisk program would put the city’s years of low-crime calm at risk.

But this big Brooklyn Bridge march of mothers, fathers and kids alters the calculus of next month’s vote. The crime issue, though important, is ultimately about self-interest.

By contrast, most New York voters—especially better-off white voters who’ve already made it here—have no direct stake whatsoever in New York City’s charter schools. They do, however, have a stake in the integrity of their political beliefs.

For decades, New York’s inner-city schools sent wave after wave of students into the world without the skills to do much more than achieve a minimal level of lifetime earnings, if that. This failure, repeated in so many large cities, remains the greatest moral catastrophe in the political life of the United States.

In 1999, the charter-school movement began in New York City with a handful of schools given independence from years of encrusted union rules and city regulations that made real learning virtually impossible in the city’s chaotic schools. The project flourished. Now nearly 200 charter schools teach some 70,000 students.

When the legislative limit on new charter-school openings arrives, New York’s next mayor will have to lobby the Albany legislature hard for permission to expand these lifeboats for the city’s poorest kids. So let’s put the politics of the mayoral election this way: Some 20,000 black and Hispanic parents and their kids would not have traveled from their neighborhoods—77% of the city’s charters are in Harlem, the South Bronx and Central Brooklyn—to march across that famous bridge if Bill de Blasio were not running for mayor. They think Mr. de Blasio is going to kill the charter-school movement in New York City. And they think this is a civil-rights issue.

One thing these 20- and 30-something parents have in common with their counterparts who live in Brooklyn’s Park Slope or Manhattan below 96th Street is that they weren’t even born when Martin Luther King Jr. gave his “I have a dream” speech in 1963. But for them, you couldn’t miss that the dream described 50 years ago at the Lincoln Memorial was alive on the Brooklyn Bridge.

A lady with a bullhorn: “What do we want? Choice! When do we want it? Now!” A sign: “Let my children learn.” And bringing the politics to the present, one sign said simply: “Charters for the 99%.”

Many voters in the parts of Manhattan or Brooklyn that have good public- or private-school options will still vote for Bill de Blasio, either because they don’t spend much time on these out-of-area moral dilemmas or they think: It can’t be that bad, can it? Bill de Blasio won’t actually kill these people’s schools, will he?

Yes, it can be that bad.

In a now-famous statement, Mr. de Blasio recently said of charter-school pioneer Eva Moskowitz: “There is no way in hell that Eva Moskowitz should get free rent, OK?” What this means is that Mr. de Blasio, under pressure from the city’s teachers union, will start demanding rent payments from public charter schools that now operate rent-free in the same buildings occupied by traditional public schools.

If the next mayor makes the charters pay rent in the city’s expensive real-estate market—essentially imposing a regressive tax on them—over time the schools’ budgets will suffocate and they’ll start to die. It will be a slow death, so Mr. de Blasio’s voters won’t notice what’s happening in Harlem, Brooklyn and the South Bronx.

The city’s charter movement has attracted innovative school operators such as KIPP, Achievement First, Uncommon Schools, Harlem Village Academies and others. For the parents who win the annual lottery to get their kids into these schools, the result is an educational environment of achievement, discipline and esprit—what any parent wants. Given Mr. de Blasio’s intentions, these innovators will start to leave the city. One of the best things New York City has ever done will go away.

Sounds melodramatic? You bet it is. Why do you think those people were on that bridge?

How Democratic politicians like Bill de Blasio and the unionized teachers’ movement ended up so at odds with the city’s black children will fall to future historians to explain. But that’s where they are. What remains to be seen, and will be seen Nov. 5, is how many New Yorkers are in that same place.

Write to henninger@wsj.com

A version of this article appeared October 10, 2013, on page A15 in the U.S. edition of The Wall Street Journal, with the headline: Bill de Blasio and Civil Rights.