Kant never says that good actions must be motivated by a sense of duty. What he does say is that actions have genuine moral worth to the extent that they are performed out of a sense duty. Many philosophers have certainly felt as you do--namely, that there is something backwards about this claim. I find it strangely compelling, and so let me try to motivate it a bit. Kant actually provides a wonderful example in the Groundwork . There he asks us to imagine someone (let's call him Joe) who spends his life doing good merely because he feels like it. He has a natural desire to help other people, and he takes great pleasure in meeting others' needs. Kant acknowledges that Joe's actions are "right" and "amiable," but he denies that these actions have any true moral worth. Kant believes that moral esteem is esteem of a very special sort. It is a sort of awe that we reserve for a select few actions and characters. But is there anything especially impressive or awe-inspiring about Joe simply...

The view you're expressing--that everything about us is caused byexternal factors, and that this rules out the possibility of free willand moral responsibility--is often referred to as hard determinism . One classic defense of this view can be found in The System of Nature by Baron d'Holbach, a leading figure of the French Enlightenment. For amore contemporary and scientific defense of the view that free will isan illusion (albeit one written by a psychologist rather than aphilosopher), try Daniel Wegner's The Illusion of Conscious Will . Hopefullyyou're also interested in reading the views of philosophers whotake a different approach to this vexing problem. If that is indeed thecase, you might want to investigate one of the many wonderfulcollections of essays on the subject. My favorite is Free Will , edited by Gary Watson for the Oxford Readings in Philosophy series. The similarly named volume edited by Robert Kane for the Blackwell Readings in Philosophy series is also...

I'm only moderately familiar with Rand's work, but one of my colleagues at the University of Michigan has a webpage devoted to refuting some of Rand's most well-known arguments. If you're interested, you can find it here .