EVERYONE IS CONSERVATIVE ABOUT WHAT HE KNOWS BEST: New York MoMA’s tough policies are an exhibit on how to maintain order.

MoMA doesn’t let you jump over the metaphorical turnstile if you don’t have $25 (you have to apply in person for your free one-year membership under IDNYC).

But the state-run Metropolitan Transportation Authority is forced to ignore tens of thousands of such chronic trespassers every day.

The MTA can’t ban people after they’ve been disorderly. Even if police arrest suspects on “low-level” charges — increasingly rare — chronic lawbreakers face no deterrence. The disorderly, and even people accused of serious assaults, return, again and again, to harass and menace paying customers.

Drugstores and supermarkets summon the police to arrest a shoplifter — only to see the thief return.

It may be time to take some enlightened inspiration from the liberal arts world: If you can’t behave, you will face the consequences.

To be fair, considering what its first curator of modern architecture was up to in the 1930s, modern MoMA seems like a healthy bastion of tolerance and inclusion for all.

(Classical reference in headline.)