How on earth do they think a business that sells food and drink makes money?
That's right - they make it by selling food and drink.
They don't make money by providing a comfortable space in which people can bring in their own refreshments and consume them.
Maybe it's because I used to work in the hospitality industry, but I find the BYO food attitude incredibly offensive.
But several talkback callers and texters thought I was the problem.
What about people with allergies, some said. Phone ahead, I suggested. Ask if there's anything suitable for people with your particular allergy.
Most cafes are very obliging if they're given advance warning of special needs diners.
Or eat before you go out and enjoy your cup of tea but don't try to have your home-baked, gluten-free cake in the cafe and eat it too.
Others complained it was too expensive to have a cup of coffee and something to eat but they wanted to enjoy the experience of being in the cafe.
Well, that is unfortunate, but tough.
When we first bought our house, we couldn't afford to go out - so we didn't.
Drinks are expensive at bars too, but you don't take your own wine or beer to your local pub and expect to drink it there.
How long do you think some gormless fool would last at Antoine's if he rocked up, sat down at a white-clothed table, ordered a beer and then opened the fish and chips he'd bought from down the road?
If he tried to complain to Tony Astle that he couldn't afford to actually eat at Antoine's - but he'd heard it was a lovely place and he had bought a beer - do you think that argument would wash?
It would not. The impertinent punter would be out on his ear so fast his chips would still be hot when he got home.
It seems very odd that erstwhile intelligent people can think it's somehow acceptable to take food and drink into a business trying to make a crust selling food and drink.
Good on the cafes for finally taking a stand and refusing to extend their hospitality to people who don't understand the meaning of acceptable behaviour.