When I cook curry I usually use about 10-16 birds eye chilis and an equal amount of fresh ginger. If dinner is spicy enough to make you sweat then it's a good meal!
Macroflation is right tho. It's somewhat about the endorphins, I think it's also about flavor palettes. In South Eastern Asia and China they mix and blend the 5 primary flavors expertly to create some really fantastic culinary experiences and spiciness modifies the impact of those dishes. If you can't handle any spice because you grew up thinking black pepper was hot you're missing out on a lot of interesting and varied cousine.