I am currently trying to figure out if there is really an afterlife and if there is, how it works. I will provide some detail below but it seems to me that both a wise God and a just after life exist. However, I don't think that there is hell and heaven in afterlife. We either reincarnate or become a part of oneness which we came from.
Shortly, Kant's Third Critique managed to convince me that there is a wise god because eventually human-beings, considered collectively, will reach the highest good on earth. And only time can tell whether the highest good on earth is being created through complete catastrophe (the scenario in which the modern civilizations are completely destroyed and a few remaining isolated communities continue their quiet life) or peace (the scenario in which bad people apologize and we come up with a new economic system that makes everyone equally happy). However, both of these scenarios, one of which must be true based on the current trajectory of the environment, imply that the highest good on earth must be realized sooner or later, which can be used to give a moral proof for the existence of God.
Now on to the highest good at the individual level, I disagree with Kant that each person will reach the highest good in an Abrahamic religion style afterlife. Kant thinks that everyone will eventually reach the highest good at the individual level even if sinners reach it later than non-sinners, but, then that would contradict the motive of contributing to the highest good on earth. In fact, that would justify the current utilitarianism approach to economics. Everyone would be justified in behaving in the most morally corrupt way possible to maximize their gains because they will be rewarded in an afterlife anyway. (Just to provide some context, Kant's God do not punish people in hell eternally. There is an end to the duration spent in hell because our sins are finite and God is fair). What Kant needs to establish instead is to confine people to this world so that everyone is affected by their own action until the day a truly happy society is established. Hence, his argument needs either one or two of the following: a system similar to reincarnation which is often found in Buddhism and Hinduism or show that we are all one and this earthly life is just an illusion and hurting someone means hurting everyone else. Through doing this, highest good at the individual and societal level would become the necessary and sufficient condition of each other and the moral proof for God and afterlife would be completed.
Last but not least, CTB must be justified in some cases considering that God is wise. So, I don't think that CTB is necessarily a sin, according to a wise God, unless it was used as a means to run away from paying the price of a terrible crime.