The vocation of doctor is a hard one. If the surgeon is misarable in his task then he has an obligation to self to seek another. Yes, there is a moral obligation to develop ones' talent, however the obligation to self is greater. If for no other reason but to aid those who come after us. The talents and abilities that we perfect or bring near to perfection adds something benificial to the world.
Actors provide a minor service, but a service none the less.
Developing their talents increases the ability to entertain. This is a service to the morale of all people at large. To provide such a thing to others is important to well being, and we all have that moral obligation to our fellow man. The only reason for this is that we essentially need each other. Man has a responcibility to himself and other men.