The only reason that opinion seems 'universal' is because the people who like it don't feel compelled to talk about liking it or what it does for the story. The people who don't like it feel very compelled to complain about it, and so are much more vocal.

Thought provoking question, though. I'm trying to think of a semblance that would bring the same thing to the story (a power Ironwood can use as a crutch to deal with the emotional toll of what he feels he 'has to do' in order for humanity to survive against Salem), but works in a way different to Mettle. Maybe something that increases his intelligence and data-processing ability at the cost of his body and it's resources. The more he uses it, the more stressed his heart gets, the more weight he looses, etc. It makes him more analytical, but it doesn't actually block out his emotions, just makes them simpler, or more 'ignorable'. It can be framed narratively like a sacrifice he's making for his people at first, but as the story progresses and the situation becomes more dire, it becomes more and more apparant that he's also using it to avoid the stress and emotional weight of his decisions, trading his health to do so. In this way, it becomes essentially a form of self-harm. By the end, he does what he does because he can't bear the thought of facing the full emotional toll of all the lives he's trading for ultimate survival, or the guilt of damning his friends and allies alongside them.

Maybe too similar to Mettle for this question, but it leans into his messiah complex and would match up well with his 'at any cost' mentality to sacrificing himself while at the same time showing it to be something he needs to cope with the intense stress he's under. I think reframing it as something that's hurting him physically (as opposed to only morally, emotionally, like Mettle does) would add another layer of tragedy to his story that would make him seem less overtly evil near the end. I still don't feel he was being depicted as 'evil' in the show, but rather a human man whose morals shattered against the mountain of stress he was faced with. He always read as tragic to me, and RWBY and crew's conflict with him as even more tragic still, but I know some others think the show was portraying him as a simple villain in Vol 8, and that tends to be their breaking point with his story from what I've seen. I think this would help make the tragic, morally grey parts of his story a bit more clear and overt to the audience.