Cash is king — but here comes the guillotine.

I’ve heard numerous stories about pennies and nickels costing more to mint than they’re worth. But I didn’t realize the extent to which debit cards, apps and other technological innovations have made paper money an endangered commodity.

It’s so bad that the city of Philadelphia recently passed a law forcing stores (with a few arbitrary exceptions) to accept cash. A similar bill in New Jersey is awaiting the governor’s signature.

I guess I shouldn’t be surprised that cash is fighting for its life. Now that I think about it, a couple of years ago, I did hear some social justice warrior on TV bellowing, “Hey, didn’t the Confederates have paper money? Let’s pour mint juleps on all the presses at the Bureau of Engraving and Printing and set them on fire!”

Ironically, merchant disdain for paper currency accelerates just as we’re on the verge of having Harriet Tubman on the front of the $20 bill. Someone will have to scramble to get around this subtle racism. (“Insert card, tap, sign…then sing three spirituals…”)

I find myself straddling the fence on this issue, which is complicated by Visa’s rewards program. (“You have 365,843,229 bonus points! That means you can hang one leg over the fence long enough to recite, ‘One Mississippi, two Mississippi…’”)

True, I pay an awful lot of bills via credit card or direct withdrawal; but I still want someone to take up for low-income Americans, seniors and the charmingly crotchety “old school” technophobes who just don’t want to change.

Ideally, I’d like to see competition come to the rescue. Like businesses that deliver your groceries or pump your gasoline, entrepreneurs could carve out quite a niche for themselves by pledging they’ll always honor folding green.

I’m sorry that greedy retailers and credit card companies have let it get to the point of government feeling the need to apply its heavy hand. Some city or state might go even more retro as they let the regulations spill over into the healthcare industry. (“Doctor, you’ll need to fill out these forms in triplicate, verifying that you are taking good care of the chickens and butter you had to accept in payment for house calls.”)

The inexorable march to all-electronic commerce supposedly saves companies money on cashiers and security; but it is also touted as blessing shoppers with faster checkout lines. No wonder — half the shoppers will be in debtors’ prison after maxing out their third card!

Technology-worshipping hipsters can be embarrassingly inconsistent. (“You can’t dwell on the past. See how easy it is for me to use an app to purchase the latest VINYL RECORD? D’oh!”)

A spokesman for the cashless movement lectured me on how the lollygaggers need to buckle down, get with the program and use a smartphone to handle all their transactions. He was going to text me with some more choice arguments, but then Verizon had a big outage.

Let’s not put all our eggs in one basket. (Especially if both the doctor and the preacher need paying.) I am no stranger to losing paper money; but at least I’ve never had anyone tell me, “Hey, you know that fiver you accidentally left on the counter? Some dude used it to clean out your mattress, your cookie jar and that tin can buried in the back yard!”