My word were "he deoesn't necessarily share the same moral compass as you". Personally my own moral compass
This is not about my or your moral compass. It's about the morals and ethics in general of developed countries such as Japan. Slavery is unacceptable in that context and people involving themselves with it are morally bankrupt. Thus there's no reason for the MC to engage in such actions, especially considering it doesn't logically follow from what we've seen untill now from him either (heck he was saving slaves a few chapters back).
Either you have to agree that his morals change based on convenience, and thus he is more of a sociopath than anything, or that this is a characterisation failure on the part of the author. Note that even in the former case, it will still be considered a bad move from the author, since retcons are not considered the greatest tool in the box. All in all, it's a misstep that was unnecessary, and is seemingly there only in order to include some staple isekai trope that "must" make it in. That's also one of the main issues with "cooking recipes" writing and isekai in general.
2.
wouldn't eventually buy a slave regardless, even if for other reasons.
The point is that it won't be facilitated by the MC, or even suggested by him. It's simply disturbing and inconsistent how he doesn't think twice about it. What's next? Gets transported to a place where it's customary to kill some newborns and he goes along with it? Maybe at that point you'll realize there's an inconsistency? Or will you?
3.
I don't expect people to hold that viewpoint,
Several pages back this was addressed multiple times, but fair enough. Just be aware that neither me nor joel hold that as a point of contention. We do not expect the MC to somehow magically achieve impossible feats, it's just jarring seeing characterisation inconsistencies just because a trope "must" make it in. I am all fine if the MC is introduced as a sociopath and then does this mind you. The problem is that the author wants to have both, which simply doesn't work (if it did you wouldn't have so many people noticing this - go back a few pages in the comments, we're neither the first nor the last to notice this, feel free to ignore people just rustled by the setting btw).
4.
what he did by buying her to essentially save her is still a net good, even if it is made to be more virtuous than it is.
I fully agree. There is nothing clashing with developed countries' 21st century morals there - his action is virtuous all things considered. That is, if he was actually feigning that he's buying the slave as a slave, and meant to just free her and employ her. The moment he doesn't do that, and instead uses her as a slave, is the moment you will have the inconsistency I spoke of. Basically his ulterior motives clash with the naturally expected morals from him. Note that he's talking about slaves as if they were objects.
just owning a slave doesn't automatically make a character a "villain"
It does make him morally bankrupt from the point of view of the morals of his original country and time. So pretty much a villain.
5.
there are people in real life who don't agree with hunting and find that to be barbaric.
Hunting is not illegal - there's a good reason for that. There are people who disagree with it, but it is not considered immoral. The same way that there are vegetarians, but eating meat is not considered immoral. Morals are a product of society, it's not defined by what a small group of people believe.
the gag argument to write something off can only go so far.
There's nothing to write off, it cannot serve as an argument for your point in the first place since it is unrelated. And yes, it us a tongue in cheek gag if you haven't noticed. He's not going around raping children.
trying to dispel the idea that he is some all round moral guy.
There's no illusion that he is perfect. But what you cited are not anywhere near the level of being fine with slavery from a moral standpoint. Not to mention that most of what you cited are not even issues morally.
to be largely apathetic to it,
He's not apathetic to it though, he's actively engaging in slave purchase, and in the future in slave exploitation. And somehow in the mind of the author this can be reconciled with what we previously saw about his distaste for slavery. Inconsistency much?
where he was pretty much ready to watch another adventuring group get killed
I just don't remember this event, so without a reference to the page I cannot comment on it. It's notable that it's still doesn't change the inconsistency that I am talking about, unless you want to argue he's a sociopath based on these grounds.
He has never been a completely good, moral person.
As mentioned - I do not have such an illusion. But there's a large jump between not a "completely good person" and engaging in slave exploitation.
when you can while also being largely indifferent.
This is not about indifference, it's about consciously engaging in morally reprehensible activities. Either he's morally bankrupt or a sociopath, neither of which follow from the text, so this implies that it is an inconsistency.
this was something the author wanted to happen
You do understand it's even worse when the author can't even realize it's an inconsistency, or realizes that, and still introduces it in order to have trope #3628 from his recipe?
oints 1,2, and 4.2: The problem is your still expecting him to act according to the morals of the period he originally came from. You say yourself that "Morals are a product of society", but for a good >15 since he came to that world he has been part of a society that seems largely fine with it. Like I mentioned in another comment, when he has been in the world for that long, it wouldn't be unreasonable or surprising for him to adapt to, or even embrace their way of thinking at this point. Also, buying a slave wasn't suggested by him, but by Fitz.
