I think the biggest reason is the concept of Karma & Rebirth. Karma & Rebirth is the only logical choice(no more Hell, thank God). This can be proven by the following examples:
A child continues to misbehave in a store despite the admonitions of his parents. Eventually he breaks a product. Does the parent simply forgive the child? Then the child learns nothing. Or do you give him a beating? Use physical violence against a child? In the olden days this was quite common, but today this action might get you jail time! So, what do present-day parents do? Today we talk to the child, make him see why his actions were wrong, have him apologize to the store owner, and then make him do odd jobs to help pay for the cost of the product. This way the child learns the right lesson, imparted by loving parents using non-violent methods. This is essentially Karma & Rebirth in action! If a Hindu were to commit an error but was unable to correct it before his death, he is given another chance to do so in the next life. He is not going to be physically punished, but he is not going to get away with his error either.
A second example: A driver makes an error on the highway resulting in horrific consequences. He dies; the occupants of the other cars survive but endure terrible injuries. They endure multiple surgeries; some of them lose their life savings and houses, and are forced to live in home-less shelters. Some religions teach that God forgives everyone, but can one be so callous as to enter heaven knowing that the victims of the other car are suffering? This brings to mind some of the henchmen of Hitler who escaped to countries like Argentina and lived a happy life while their victims were left to deal with the pain and suffering.
What if God gave you a choice? Either go to heaven or be reborn and maybe help the victims of the car accident or others in a similar situation? Which option would you choose? For me, honestly, there is only one option. Karma & Rebirth is the only logical choice.
But lets not lose sight of the bigger picture here we may never know if Karma & Rebirth can be proven to be occurring - these concepts are teaching us to accept responsibility for our actions, do the right thing! If you made an error, dont run away, stand your ground, accept responsibility, take the criticism, then go out and take steps to correct the situation!
The concept of Karma & Rebirth also do away with the notion of Hell a barbaric, abusive place unworthy of God. Evil men like Saddam Husain and Stalin used to run torture chambers, and we think God uses their brutal methods? God buys love with threats of torture? But if we are uncomfortable with the concept of Hell, then we must do away with Heaven also. It does not make sense for Pedophiles, murderers, Abusers and the like to simply walk into heaven.
Anyway we look at it, Karma & Rebirth is the only logical choice
