Why can't my roommate eat spicy food at all and say that not eating spicy food is the embodiment of health, wisdom, peace and justice? Is there any scientific basis for this?

I think your roommate is simply relying on his little cultural knowledge to make excuses for himself. He likes to eat Chili, which is a person's taste. Some people like it, others don't. There is no basis at all. You can also tell him that people who like to eat Chili peppers are a symbol of courage.