What would our world be like if we ceased to worry about 'right' and 'wrong,' or 'good' and 'evil,' and simply acted so as to maximize well-being, our own and that of others? Would we lose anything important?
Ethical ideas and sentiments have to be considered as parts of the phenomena of life at large. We have to deal with man as a product of evolution, with society as a product of evolution, and with moral phenomena as products of evolution.
Human well-being is not a random phenomenon. It depends on many factors - ranging from genetics and neurobiology to sociology and economics. But, clearly, there are scientific truths to be known about how we can flourish in this world. Wherever we can have an impact on the well-being of others, questions of morality apply.