I'm with you on this as well.
It is private property and the owners should be able to exercise this option.
Trouble is, the FCC has outlawed cell phone blocking devices in this country. You can order them from a British company that I'm sorry to say do not have a link for.
I've done some casual 'consulting' with several friends who happen to run restaurants and such and those devices would be a Godsend for the atmosphere that they are trying to create.
My 2 pennies worth.
That's true. Passive interference, i.e., shielding, is legal. But it's expensive and tricky to do right.