Why do certain groups/clubs insist on "hazing" or initiation rituals?

It's a sociological issue. Why do people do the things they do? Hazing helps bind the group together and builds group cohesiveness. It's a form of bonding (like wearing a uniform or having the same tattoo). Even primitive people have initiations rituals. It can be a valuable tool or it can be childish, primitive and dangerous. It can become a form of bullying and it can be abusive. It's all about power and control. Avoid such groups if you can. If you feel you need the social support, do it, but be careful. And if you end up in a group and you feel like you are at the bottom of the barrel and you are not getting any respect think about leaving the group. The relationships you develop now may follow you for many years. If the relationships are negative and not beneficial - leave. Don't waste your time with such people. Life is short.