BETHANY MANDEL: The left is a cult — and parents can fight it, with Supreme Court’s blessing.

In a landmark ruling last month, the Supreme Court slapped down a public-school district’s mandatory lessons on sexual topics for young children — and gave parents the power to push back against leftist indoctrination in school.

In Mahmoud v. Taylor, parents in Montgomery County, Md., argued that mandatory teaching of LGBT-themed books violated their families’ religious beliefs.

They didn’t seek to remove the books — only the right to opt their children out of lessons that used them. The court backed them.

The district’s instruction promoted the idea that gender is fluid and interchangeable, a notion that runs against the teachings of every major monotheistic religion: Judaism, Christianity and Islam.

Its LGBT teachings are part of a secular belief system that deliberately aims to supplant those traditional faiths with a new one.

Leftism today increasingly functions not merely as a political ideology but as a full-fledged secular religion, complete with its own moral code, dogmas, rituals and rules of excommunication.

For example, “Consider any discussion of climate change. Suddenly, leftists become apocalyptic preachers warning of imminent destruction: rising seas, burning forests, uninhabitable cities  — all brought on by sinful human consumption.”

When the late Julian Simon debated an earlier iteration of hard left religious eco-zealots, he had this classic reply:

Simon, the economist who was legendarily skeptical about environmental doom, once posed a question at an environmental forum: “How many people here believe that the earth is increasingly polluted and that our natural resources are being exhausted?” Almost every hand shot up. He then said, “Is there any evidence that could dissuade you?” There was no response, so he asked again, “Is there any evidence I could give you—anything at all—that would lead you to reconsider these assumptions?” Again, no response. Simon concluded, “Well, excuse me. I’m not dressed for church.”

Heh, indeed.™