Alright guys. Lets keep personal attacks out of this. If the OP wishes to keep his betta in a bowl that is his choice. All we can do is provide information for him to make an educated decision.
To the OP, Bettas thrive in warmer temperatures (80f). It can be hard to keep the temperature of a bowl at a constant 80f because of the small amount if water. Smaller bowls can be harder to keep clean. The combination of dirtier water, ever changing temperature and the lack for proper places to rest and hide can cause stress for the fish. Stress often results in a lowered immune system that then leads to disease. Fin rot and bacterial infections being the most common.
Although it is possible to keep a betta in a bowl, the over all health and well being of the fish is compromised in such a small space. Most of the members of this forum believe in giving their fish the best possible living conditions which evolves supplying them with larger tank, places to hide, clean water and adequate nutrition.