This is called a false dichotomy. It is a fallacy, and I can see how you can get from this fallacy to your poorly considered notion of morality.You can only become, say, and anthropologist or a philosopher. Only one. What one will it be?
But, I can correct it easily:
For instance, I was spending some time a while ago correcting an anthropology textbook, since the concepts were weak, so I can do both.
I could also do neither, and many people would say that since I'm getting a degree in neither, I am doing neither.
Now, since I find anthropology to be insane (I said, I was correcting a textbook), I will not do it. The conceptual foundations of the discipline are weak. However, I understood and, quite unfortunately, memorized quite a few of these concepts that I corrected --
I weigh the cons of one half. Now, I can weigh the cons of philosophy. And I can weigh the pros. I can extrapolate consequences. Then I make a decision, and this decision will be rational, and based both on my values and on an assessment of the situation. This is how one makes moral choices: not from inability, but from insight.
Your pseudo-Nietzschean idea that the only reason I'm not doing anthropology is because I can't do it, is quite a bit of a stretch.