Interstellar Plan B

In the movie Interstellar Plan A is to bring the human race to a habitable planet, and if that is not possible, then Plan B, which is to bring embryos and start a new human colony. My question is why must they do Plan B? Why does the team feel obligated to continue the human race? Plan A makes sense because they want to survive, but if they cannot survive, why must they ensure that human life continues? The embryos have not been born yet, and have do not have a want to live.