Everything we consider good and bad right and wrong was decided by someone long ago. So it is all a matter of opinion. Is shit a bad word? Someone thought it was long ago so now we do. Is stealing wrong? Someone long ago thought it was and prohibited it. Everything in our lives tradition, rules, laws, ethics was decided by a human being at one point, it is all opinion.
If you let a child grow up with absolutely no rules they will think nothing of stealing, killing or anything else we hold as wrong. A child will take without permission until they are taught not to, they will hit, bite, yell and have fits. You may not think for a second divorce is unethical but many do. All opinion.