It is rational to choose the right means to your ends to develop very elegant abstract formal theories of rational choice, and then turn these into what look like moral theories. Philosophers tend to be ravished by the formal beauty of such theories, and they don't pay much attention to the fact that our human limitations make them pretty useless in practice, while the simple point about instrumental reasoning is too shallow to be of much real moral interest.

Kant's aim was to develop a religion within the boundaries of mere reason (that is, reason unaided by special empirical revelation) and then to ask about existing ecclesiastical faith (especially about Christianity, and the Lutheran Christianity of his time and place) how this revealed faith must be interpreted if it is to be reconciled with reason, and even seen as a wider (though morally optional) extension of a religion of reason.

It is absurd for anyone to think that Soviet "Marxism" is a correct application of the thought of Karl Marx. No doubt Soviet propaganda represented it this way. But who believes Soviet propaganda? It is remarkable (but maybe not so remarkable after all, when you consider their motives) that apologists for capitalism, who would not accept Soviet propaganda on any other point, are eager to agree with it on this point.

It is probably not a good idea to ask someone to expound a position they do not accept and do not feel they even fully understand.

The problem is that many who reject Marx do not read him, or read him only by bringing prejudices to their reading that prevent them from understanding him.

Kant considers belief in God and immortality to be items of "faith" because he relates faith to the pursuit of ends - in this case, the highest good.

Adam Smith was aware of the way that economic interests could have a distorting and destructive effect both on the market and on politics.