I went with “subjective" because it's just easier to prove. I'll define “wrong" as “I REALLY don't agree with this behavior." Since I don't approve of coercive sex then it's wrong. If child rape violates some law of the Universe, then how does it happen? Nothing in the Universe stopped it from happening.
It's repulsive to me because I feel empathy for the victim. Sociopaths don't feel empathy.
'Charity - yay'
'Rape - boo!'
'imprisoning rapists - 'yay'
although cultural relativism can be a bit silly non-cognitivism is a much more powerful adversary to naturalism - essentially moral claims are neither true or false because they are not really propositions - they are not truth-apt, it does surprisingly well at explain how morality 'works,' where it came from, how we change it.
however like relativism it does not preach tolerance - just the opposite in fact it leads to a war of ideas however non-cognitivists have methods of making you change your mind about moral issues - relativists do not have any such mechanisms.
The concept of rape itself is bad already in all places. Objective
It is objective based on that there are absolute truths and morals to live by, and though we decide if we believe them or not, that doesn't change the reality that they are truth.