I'm sceptical about Rugani myself, but calling out mistakes which could have cost us doesn't qualify as hate, does it?
On the other hand, i get the feeling there are users who actively chose to rate him, solely based on their personal dislike for Bonucci.
I wouldn't say that's hate at all. Linebreak, Juliano13, and a few others call him rubbish (or worse) often. That's hate.
I think Rugani makes mistakes that most young defenders make. However, something I have noticed with him is that he most often recovers very well from his mistakes and seems to learn from them.
We also have an amazing defensive record with him, so he must be doing something right over the course of games. He makes very few bad mistakes imo, but because he's young and trying to break into our starting XI for a significant period of time now, he's under the microscope for every little thing he does on the pitch (same deal with Bonucci though for a different reason, an irrational personal dislike for him).