Hedonism Kant Be The Way, Can It?

In a universe increasing less black and white and enjoying more grey, I pause to reflect on the concept of Christian Hedonism.

I have always appreciated the more rigorously fashioned ethics of Kant, an action is either right or wrong, all times all places in the universe. One does not do the right thing out of hope for a reward, only of the duty that knowing the right thing to do compels one to do the right thing. The difficulty is discerning or revealing an actions’ inherent evil or righteousness. But there is no room in his logic for an ambiguous action – only the certainty of judging an act objectively as right or wrong. Straightforward, an action either is or is not right. Our appetite for a reward or aversion to punishment is irrelevant. Period.

Now I read about CS Lewis and he shakes me up a little bit about something I was certain – hedonism is a bad thing. Lewis reflects on an objection to Kant’s matter of fact denial of hedonism:

British writer C. S. Lewis, in an oft-quoted passage in his short piece “The Weight of Glory,” likewise objects to Kantian ethics:
If there lurks in most modern minds the notion that to desire our own good and to earnestly hope for the enjoyment of it is a bad thing, I suggest that this notion has crept in from Kant and the Stoics and is no part of the Christian faith. Indeed, if we consider the unblushing promises of reward and the staggering nature of the rewards promised in the Gospels, it would seem that our Lord finds our desires, not too strong, but too weak. We are half-hearted creatures, fooling around with drink and sex and ambition when infinite joy is offered us, like an ignorant child who wants to go on making mud pies in a slum because he cannot imagine what is meant by the offer of a holiday at the sea. We are far too easily pleased.[2]

So, ought we do the right thing because there is a reward, or not? Can it be both ways, do it because it is right AND do it because a reward is there?

Why ought we do the right thing?