I found this manga to be a very fun read. For once, we have a badass protagonist that, while a bit edgy, actually gets some real revenge. It's a breath of fresh air. I only wish he was even more crazy and driven. I feel like his motto of not killing those who've not offended him or whatever to be unnecessary since he's so unhinged already, not that it seems to stop him from killing random people whenever necessary. I guess I wouldn't want a protagonist that just actively goes around killing everyone for no reason. It feels like he mellows out a bit after a while, but I guess that's not too unexpected with how the setup leaves little to take revenge on in the end and the revenge targets drop pretty fast. Not the best foresight from the author but I didn't expect that much since the story isn't particularly well thought out, clever or well written, it's mainly just a clump of fetishes, edginess and wish fulfillment that just happens to be good enough on its own with how starved a lot of people get for that after reading other trope novels/manga.
This is a great example of a very polarizing manga. On one hand we have the snowflakes that just can't quit raging about something that go against their moral values and fetishes actually existing and then we have the people who mostly consists of those that have read and seen so much shounen bullsh*t and other tropes where everyone's a saint, doormat and incredibly unrealistic that they revel in this kind of story.
This manga is aimed at those who find the power of friendship offensive, who hates when protagonists bring their modern day values into a foreign primitive world to "educate the inferior apes", those who prefer their protagonists to kill someone instead of leaving seeds of trouble, who has no qualms about adapting to a new world, where it's not a matter of forgiving those who have wronged you but letting them face the consequences of their actions instead, where people act like trash and deserves to be trashed for that cheap satisfaction of us readers finally seeing the trash taken out. Where the protagonist actually acts human to some extent instead of being mr goody two shoes.
Basically, it takes the idea of a doormat protagonist, chucks it out the window and instead embraces sadism and vengeance. Where your teammates are eternally loyal in one way or another and they don't get to tell the protagonist what to do.
Honestly, I think a lot of people who really enjoy this are those who are simply tired of the generic tropes. At some point, people end up so pent up from frustrations of protagonists acting like imbeciles or gullible children that it backlashes to the point of an edgy manga like this becomes an awesome read, even if people realize that it's not a particularly good one story wise, but it clicks so many of the right buttons and fills a void from other stories.
It's not necessarily about people enjoying rape (and let's be honest, seriously, whom among us has never read some of the countless hentai manga of the forced variety, don't kid yourself, it's just human nature), it's about the idea behind it all. The rape is just a small part of the big picture that's painted, just because you don't like it doesn't mean it wouldn't exist in any world, especially a primitive one and EVEN MORE SO when people can get overpowered with no real laws binding them. To turn a blind eye to reality is just pitiful. In a world like that, taking in a slave might as well be saving them if you treat them decently. Let's not even begin the argument if him taking some girls as followers instead of killing them by use of some measure of mind control is better or worse. It has no clear answer and I personally believe killing would be worse.
Oh, and even if people do enjoy those aspects, get off their backs, people are free to have whatever fetish they want. Humans with no unsavory hidden fetishes or fantasies are few and far between. They're just that, fantasies. Unlike your typical beast, humans at least know that it's just a fantasy, just like how we like killing people in a video game but don't go out on a shooting spree. It's healthier to fulfill than ignore fetishes as long as we keep it imaginary.
My point is... Get out of here and stop leaving bad reviews if the reason you're doing so is because you didn't like the basic concept of the story. A few chapters in, it would be clear that it was a miss. People here are pretty much the same as an adult reading a shounen manga leaving a rating that it's not adult enough, people reading a shoujo manga and complaining it's not masculine enough, reading a horror manga and leaving a 1/10 for not being slice of life and heart warming enough or why not a comedy gag manga and complaining it's not serious enough. Hell, it's like reading a drama tragedy and complaining it's not jovial and light enough.
What are you even doing here? Go find something else instead of cracking down on a manga as if it owes you to be as you expect it. I do realize a lot of mangakas have painted an unrealistic expectation of this genre of revenge and so on, by being all like "oh, he was betrayed and want reveeenge" and then he ends up being a god damn saint doormat that drops the revenge as fast as his dignity. But if you read the tags "rape, abuse, abused male lead, rape victim/s, antihero, borderline H, sexual abuse, slaves, torture".... What do you expect? No, really, what the actual screaming F do you expect? Why even bother reading if these tags offend you so much?