I think people who hate on Tooru don't just misunderstand the character but also ignore the narrative structure of Jojolion and what the story truly wanted to tell.
Because Tooru as the main villain, given what he represents, his relationship with the cast, and so on, was just perfect for the story that Jojolion was telling. He’s the quintessential rock-human, with the explanation of his birth process, and how his philosophy perfectly captures how rock humans think. He’s the personification of curses and calamities, which has been hinted at pretty much from the start (and he’s also literally targeted some characters in the cast since they were kids, and the Higashikatas since Radio Gaga), Now, sure, you’ll say that representing symbols or concepts from the story isn’t enough to make a good character, and you’re right but he’s also exceptionally well-written as a character, with an awesome symbolism and dynamics, etc. (I don’t really feel like doing a full analysis here, so I’ll stop there, but you get the idea). I hear a lot of people say that Jobin should have been the main villain etc but when I, aware of what the story is trying to tell, when I hear that, I say to myself, "But that would be bad on so many levels narratively, contextually, just so many”. I get that was thet pretty major antagonist of this part, they’ve seen his evolution, they’ve grown attached to him, etc yes, but narratively speaking, it wouldn’t make any sense. Jojolion is a story about breaking a curse, so does that mean Josuke is going to fight his brother, his own family, even though they just have conflicting values? No, that doesn’t make any sense; it wouldn’t fit with what Jojolion has been trying to tell from the very beginning of the part. The real enemies in this part are the rock humans so rokakaka organisation, but above all how curses and calamities impact peoples. And who is already responsible for that, but also the pinnacle of it all? it's that fckn damn Tooru. In my opinion, given everything Jojolion has established with its story, in the end, the only villain who could have the main villain of this part is inevitably a Tooru-like or at least someone who comes close to him in some way. So I’ve come to the conclusion that if you didn’t like Tooru, you’ve indirectly, implicitly, without even realizing it, already failed to understand what the story was trying to tell, but also didn’t necessarily really like what Jojolion was telling as a story. (Actually, that’s a bit of a stretch, you can still like it even if you don’t like the antagonist, but in that case it’s a bit of a special situation. Anyway, you get the idea.)