Social and legal obligations often originate from ethical frameworks. For example, human rights were initially a purely ethical concept which most white people

Social and legal obligations often originate from ethical frameworks. For example, human rights were initially a purely ethical concept which most white people at that time thought to be ridiculous. And now it is a social and legal obligation in all Western countries to treat every human equally, regardless of skin color or religion. So by abandoning ethics you are actually cutting off a source for improvements of our social and legal norms. I'd also would like to point out that it doesn't follow from being constructed that something is 'merely fiction'. Everything in humanities is constructed (and some would even argue that everything in science is constructed). The question is: does it impact our lives? And ethical reasoning obviously does it.