I just brought home a bean soup from a local Pizzaria. The flavor was delicious but I threw most of it out because the beans were tough. I find under-cooked beans in all sorts of restaurants. Besides having an unpleasant texture, chewy beans are challenging to the digestive system.
I suspect this problem is due to cooks' ignorance of a simple fact: Salt and acidic ingredients will toughen the bean. I learned long ago that if you want beans to cook thoroughly, hold off the salt, tomato, celery, and citrus until after they've gotten soft.
But perhaps I'm the ignorant one... Do some cultures prefer al dente beans? I don't think I've ever had a tough bean in a Carribbean or Portuguese restaurant. But many Italian, American, and Natural Food places have served me chewy beans.