In this specific case I agree, not reporting CSA should be illegal (and probably is?) I’m not so sure that we should codify the current ethical understanding into law though.
We need to leave room for development. Forcing new ideas to first go through the battle of legalization isn’t helpful in this regard. Laws are there to regulate what normal social regulation can’t do properly.
I think people who cheat on their partners are morally speaking bad people. But writing into law you can’t have multiple partners at once is quite obviously a bad decision, because there are happy polyamourus relationships. The government doesn’t need to get involved here, being treated like the ass that you are for cheating is punishment enough, and leaves the room for developing new ways of living together.