It’s nightmarishly grotesque, and horribly revealing, that crowds will gather in New York and other cities on the third anniversary of the Oct. 7 atrocities to celebrate the mass slaughter of Israelis by the “Islamic Resistance Movement,” a k a Hamas.

Not to protest Israel’s actions before, during or since the war those attacks began, but to cheer the 6,000 or so who invaded the Jewish state to kill, rape and kidnap civilian kibbutzim and dance-festival ravers — and filmed it all, instantly sharing it with their victims’ families and the world.

Why else gather on this day, the high mark for the terrorists and their cause?

The organizers, including the “youth section” of Mayor Zohran Mamdani’s beloved Democratic Socialists of America, say it’s because the date “marks three years since resistance against imperialism changed the fate of our world forever.”

Again, the “resistance” that day was purely a matter of terrorizing innocents, and Hamas’ least-shameful actions since amount to nothing but losing to the Israeli forces that moved into Gaza to recover the hostages and smash the terror infrastructure.

The only imperialism to be set back here is the one run out of Tehran, whose pawns in Gaza and Lebanon have been eviscerated and its catspaw in Syria removed entirely.

But the rally-goers mourn all that; it’s the Jew-killing they dig on.

In a sane city these death cultists would face condemnation from even center-left Democrats, the ones who used to retain a shred of principle and pretense of respectability.

But they flushed away those last scraps of decency as the party’s hard left won some primaries: When you stand for nothing except holding power, you’re obliged to bow to the barbarians you need to keep it.

So the Democrats — and the global left — have embraced oblivious sanctimony, insisting against all evidence that Israel’s just war against Hamas is a “genocide.”

They just plug their ears rather than hear the debunking of all the lies about famine, the bombing of hospitals and the wholesale slaughter of civilians lining up for aid.

Western elites laud and applaud “NAZA” — a sham documentary that smears the IDF’s conduct of the war — oblivious to the multiple vigorous, scrupulous debunkings of its anonymous, unsourced and fact-free claims.

Then again, most of these same “well-educated” fools fall for the old lie that Israel is a racist settler-colonial nation, built on the dispossession of indigenous people — when its population is mostly descended from Jews whose ancestors never left the region, though many others were driven to Israel as the Arab states expelled them after 1948.

Barack Obama, the moral center of the Democratic universe, has joined the rest of the party elite in embracing Abdul El-Sayed, the Michigan Senate candidate with family and financial ties to terror-related Islamist outfits, who blares the “genocide” lie even as he adamantly refuses to denounce Hamas or the Iranian regime’s slaughter of tens of thousands of democratic protesters.

Mamdani, in the name of combatting antisemitism, is funneling public money via various fronts to the pro-Hamas Council on American-Islamic Relations, among his other services to the forces of hate.

Yes, the mayor condemns Oct. 7 as a “war crime” — yet that’s still pro-Hamas spin, as the attacks were a breach of peace that caused the ensuing war.

It’s a celebration of terror on New York’s streets on Wednesday, pure and simple — and anyone who tries to explain away that obvious truth is siding with the genocidal butchers.

Opposing the death cult is a pretty simple test of conscience; it’s sad to see how many fail it.