SwishDrip It depends. If the author intended for the main character to be a caricature for a parody story where he's making fun of certain tropes and thus deliberately has the protagonist behave stupidly (for slapstick humor), then I guess it's okay.
But these sort of reviews seemed done out of malice, to bash the story/protagonist, which just leaves a bad taste in my mouth. I get it. The protagonist is not a real person. That's fine and all, but it still feels unpleasant seeing people ridicule him. As much as the protagonist or characters are not real, the insults and malice on the other hand feel genuine. And that's why I can never bring myself to find it funny.
I don't know if this is meant to be a suitable analogy. If you see someone punching a punching bag, that's fine because you know a punching bag is designed to take punches. That's why it was produced in the first place. On the other hand, if you see a malicious child throwing toys around and breaking them just because he doesn't like them, it feels...unpleasant. Okay, perhaps the toy isn't some Master Grade Gundam model kit where the guy put in a lot of hard work to build it, but that's besides the point. It's just the witnessing of wanton destruction or violence (and here I'm looking at verbal violence), and I feel for the toys more than the kid throwing a tantrum.
If the characters are designed to be hated (like villains, antagonists, etc. where the author makes sure he commits every despicable act of evil under the sun), then I can understand why it's funny when people bash them. That's what the author intended, after all. But when he's just a poor writer or because the main character doesn't do what the (generally juvenile) readers want him to do (generally killing enemies or some edgy nonsense), they start throwing around words like "incel", "retarded", "loser", "spineless" and "pathetic. If the main character is nice to girls, they throw around the words "simp" and "beta". How exactly is that funny?
To me, it isn't. Honestly, if the writing is poor, there are other ways you can make fun of the writing or the main character without just blatantly dishing out insults. That's why I find the reviews I found funny. They don't go overboard, and they don't even resort to insults. That's actually pretty impressive and the kind of criticism that's more constructive than just throwing a tantrum and bashing the main character for not being edgy and psychopathic and misogynistic.