In the 2 years I've been playing, it has been explained that decapitating, skinning and collecting body parts of sentient beings for this purpose is an evil act. Since the group is assisting him 90% of the time with the collecting, via chopping and cutting these beings up, they are also performing evil acts. They're also not arguing or trying to stop his picking at brains. He talked his way out of it without getting a scolding. Over time, I'm planning on a group alignment shift if they don't come to the realization of what they're doing.
Wait, wait, wait.....
So storming into a sentient beings home because they are "evil" and you heard they have treasure which you are going to take after you finish slaughtering each and every one of them is "good" and perfectly normal and acceptable....
But doing anything to the body after the being is dead is evil?
So causing pain and harm to a still living being=good
Doing harm to a dead being= evil
You have one really screwed up moral system there. Once you have already crossed the line of "I don't care whether they are sentient, I am going to personally kill these beings without any sort of due process and I really don't give a damn what the rest of their people who might have any emotional attachments to this being think, I will kill them if they get in my way or try to attack me too" in what perverse way does it actually matter to any degree what exactly is done to the body once the actual spirit of the being has been snuffed out?
You have already decided it is entirely moral to kill a minotaur for being a minotaur, if someone decides to dissect the body out of curiosity... who cares? I mean, seriously-- are you a catholic living in the dark ages or something?
Yes, in our real life society dealing with humans, we tend not to desecrate bodies after death (granted, every culture has a different idea of what should be done with the body) but that is out of respect of the people connected to that person... In real life there are no peoples who every single individual of those people we see we can instantly determine upon first glance that they and every other one of their people is absolutely "evil" and needing of extermination unless they do something massively abnormal and demonstrate otherwise. D&D simply abhors the level of complex morality that would allow us to deal with things like this rationally... By intrinsically declaring there are universally "good" races and universally "evil" races with only ultra rare exceptions, suddenly issues like this don't make sense.
If you could say "well, this minotaur who was evil was one out of 10,000 who went on a murdering rampage and if we let someone decapitate him and dig through his brains, it might offend his wife, children, brothers and sisters, etc. who have never done ill towards others and even his evil acts could probably be explained as the results of rough experiences or indoctrination screwing him up." that would be one things-- but if you are playing in a game where "He was a minotaur and in our way and attacked us, so we can be certain he never did anything but evil deeds in his entire existence and us snuffing out his life was righteousness" and also note that we can determine simple from it being a minotaur that it was a "he" because practically always evil races are always depicted as exclusively male while any evil races that regularly feature females are redeemable. Because D&D is built out of that sort of mindset.
But, really-- even then that doesn't always hold up, in wars up to modern times soldiers macabre collected body parts of their slain foes. It can't even be really classified as particularly abnormal. So we can demonstrate that when a group is in a position to classify an entire other race as "evil" desecrating their bodies and taking trophies still falls under a moral umbrella that few would be daring enough to insist is absolutely "evil"-- rather, it seems like a totally neutral act.
