There’s very loud minority that hates Mushoku for who MC is, because they can’t stomach the fact he’s not a self-insert character, and they tend to raid every Mushoku-related thread on the net. Some people just can’t understand that bad person != poorly written character. Of course, there are those who raise valid concerns with the story, but from my experience, they’re a small part of that group, and if you look at the actual numbers, you can see that MT is very popular.