GP clearly uses a deontological line of thinking on this matter. Something that GP considers to be "inhuman and barbaric" invokes a line of thinking in where he/she believes one ought to not do a certain action, because it simply is wrong.
I'm not the best at explaining deontological ethics, nor are the people who think like this. My point is: a lot of thought has gone into the types of statements that GP makes, and IMO it's worth thinking about.