[unishark]

> Why is reducing suffering ethical?

Deep question. Seems like it's usually more of a postulate of ethics than a logical conclusion. Treat others as you'd like to be treated, for example.

If you're looking for a scientific answer, it's probably that empathy makes you suffer when you see it in others. And empathy is instinctive behavior that presumably evolved for the good of the species. Though evolution might be "selfish" in its own way, preferring to protect some species which are useful to us in other ways while eating others.