Rikers Island is a dangerous cesspool of violence, corruption and inhumane conditions. There’s absolutely no question that it should be shuttered.

But there’s also no doubt that closing Rikers is tremendously complex. It’ll take far more than a lofty election-year promise from Mayor Bill de Blasio, who just a year ago said the notion of closing the jail was unrealistic and who on Friday rejected the idea of placing new jails in every borough instead of having it all at Rikers.

Closing Rikers will require a detailed plan, and a mayor and city officials determined to execute it.

Now, we have the first part. Jonathan Lippman, the state’s former chief judge, led a commission that developed an extensive 148-page proposal. To reduce incarcerations, the report suggests controversial moves, such as ending the use of monetary bail before an accused person can be released, and instead reforming how decisions are made about each defendant pre-trial. Another is decriminalizing offenses like prostitution. And the proposal calls for a community jail in each borough. The report dives into everything, from what new or refurbished jails would look like and how much it would all cost ($10.6 billion) to how Rikers Island could be used in the future. (Think an expanded LaGuardia Airport or a new waste-treatment plant.)

But by most accounts, de Blasio didn’t even read the plan before embracing its conclusion. And he is already picking apart and backing away from the specifics. That’s not an auspicious start to this intricate undertaking.

De Blasio has to lead because doing what’s right won’t be easy. Any effort should start with reforming incarceration, bail and the jail system. It will mean fighting to change state laws, such as eliminating financial bail. It’ll mean taking on the corrections unions, which have contributed to Rikers’ poisonous culture. And, it’ll mean convincing residents that community jails will work and belong in every borough.

Rikers is a dark mark upon NYC. To close it in a decade, city officials must start the process now. Creating a humane, modern and safe jail system for inmates and officers, combined with a new approach to deciding who should be behind bars and for how long, is the goal.