Well, look at places like Jamacia, Mexico, Thailand, India, some parts of China, and etc. Now, with that said I would caution against jumping into spicy food and say, putting bhut jolokia powder on everything you eat when you are not used to the heat, but I have yet to see a definitive peer reviewed study that will pull me away from the peppers. I see far more studies claiming the benefits of peppers than condemning them.
It's been proven hot peppers do not cause ulcers, but they will irritate existing ones. If you have no stomach illness or chronic stomach pain (IBS, Chrones, ulcers, etc) then I have yet to see anything that says hot peppers are bad.
With that said, I have read that they can irritate your intestines if you eat too much, so I would introduce them to your diet slowly. There is no shame in starting with jalapenos and working your way up to habaneros and etc.