Another specific. Kant rejected the ontological argument for God, an argument going back at least to Aquinas and his Five Proofs for the existence of God and also as presented by Descartes in both his Meditations and his Method. Kant, however, did not go the way of Spinoza or Hume, but instead formulated a new argument for God. A moralistic argument.
It goes something like this.
(1)Reason has a sense of right and wrong.There's nothing formally wrong this argument. Informally, however, I think there's plenty wrong to point out.
(2)This sense holds within it the idea of justice.
(3)Justice is never attained or actualized in this world.
(4)Therefore, there must be a world after this and a perfect judge in that world who will make sure everyone earns his just rewards (and punishments)
Premise (1) I won't deny. Human beings clearly have a moral sense. The origins of this sense, though not directly addressed by Kant, are an important issue. The evidence before us today points to a natural origin of morality. The evolutionary benefits of such a faculty are clearly demonstrable. And in our closest cousins, the great apes, we observe a similar faculty in operation. They work together in a community. (For more on the evolution of morality, I recommend Dawkins' The Selfish Gene.)
Premise (2) is also not a problem. The human mind has obviously constructed an idea, we generally call it "fairness", where good deeds are rewarded, wicked deed are punished. And I think we'd all agree with premise (3) that this idea is never actualized. Good people get hurt all the time. Bad people sometimes end up doing quite well for themselves. As all our parents probably told us a hundred times: Life isn't fair.
And Premise (4) is not necessarily flawed. If fairness must be achieved, I agree that there must another world wherein dwells a powerful judge. But what reason is there to think that fairness must be achieved? The ontological argument (which Kant was decidedly against) would say the idea must exist somewhere since we have the idea (living post-Kant, this probably strikes all of us as silly prima facie). But beyond the rejected ontological argument, there is no reason to assume that fairness must ever be actualized. There is only the self-centered, arrogant longing of human beings, who feel themselves unjustly wronged, for some form of ultimate vindication. "That kid stole my lunch money and got away with is. But some day God will make him pay."
I have to wonder if Kant's parents never told him that life isn't fair, or if, perhaps, Kant simply never listened.
There's another element at work here. For Kant, there must be a designer (and therefore, design) because that is the only explanation for the world that establishes not only why it is possible for the world to be as it is, but why it must be that way. Kant and others are not satisfied with explanations that establish only the possibility of the world being as we now see it. Obviously, they would have all sorts of problems with modern science. Evolutionary theory, for example, makes it very clear that homo sapiens are not a necessary result of evolution. Quite the opposite, any one species is statistically a very unlikely result. Had the first vertebrates died out millions of years ago, none of us would be here. It's the same story with languages. There is no reason why modern Midwest American English (my native tongue and dialect) needs to exist. Languages, like organisms, arise through blind natural processes.
I suppose it's comfortable and flattering to believe human beings are the pinnacle of evolution (or of God's/the gods' creation, if that's your cup of tea), but the evidence doesn't point in that direction. Such a conclusion is the result of hubris, not sound reason.