Setting aside the genuinely interesting talk about the philosophy of nature and what i goodor evil in relation to it, that stuff actually has no bearing on Ethel. Hags aren't representatives of nature, not really. They're as inherently, innately cruel as any demon or devil. They're sadistic, treacherous and manipulative. They're not some neutral force that will leave you alone if you don't cross them. They manipulate and tempt and trick. She wants Mayrina's baby to eat it and turn it into another hag. Sure she can be avoided, sure Mayrina had other options, but that doesn't change the fact that Ethel WANTS to be cruel, wants to hurt and corrupt at every avenue she can. That's like saying loan sharks or predatory lenders aren't evil or immoral just because you can avoid them. They still prey on the weak and defensless, the unwise or the poor and desperate. Even in her lair we find a dwarf that she tricked so that he made a deal with her.
