What is our purpose? Well, we humans are as conspicuously different from other animals as the anteater. In our case the distinguishing feature is the ability to reason. So obviously that is what we should be doing, and a human who doesn't is doing a bad job of being human — is no better than an animal.
I say pick b. No one knows who said "never attribute to malice what can be explained by incompetence," but it is a powerful idea. Its more general version is our answer to the Greeks: Don't see purpose where there isn't.
Or better still, the positive version: See randomness.