If you choose a profession that doesn’t arouse your everyday passion for the sake of serving instead some abstract faraway good, you might end up as a person who values the far over the near. You might become one of those people who loves humanity in general but not the particular humans immediately around. You might end up enlarging the faculties we use to perceive the far — rationality — and eclipsing the faculties we use to interact with those closest around — affection, the capacity for vulnerability and dependence. Instead of seeing yourself as one person deeply embedded in a particular community, you may end up coolly looking across humanity as a detached god.
Third, and most important, I would worry about turning yourself into a means rather than an end. If you go to Wall Street mostly to make money for charity, you may turn yourself into a machine for the redistribution of wealth. You may turn yourself into a fiscal policy.
But a human life is not just a means to produce outcomes, it is an end in itself. When we evaluate our friends, we don’t just measure the consequences of their lives. We measure who they intrinsically are. We don’t merely want to know if they have done good. We want to know if they are good.