Huh this is quite a debate. I'm not going to try to quote because it's just too involved at this point.
My viewpoint on how-much-can-we-blame-on-Hojo is that, based on the one reminiscence to his childhood we get from Sephiroth, Hojo was a major presence in his formative years and he was emotionally abusive. I'm not sure Hojo
can interact with people without being emotionally abusive, but obviously it's worse for a small child.
It's not
normal for a caretaker's reaction to a phrase like 'mysterious power' being insufficiently scientific to be such intense rage that you're still vaguely traumatized by the memory like twenty years later, after fighting a war. (It's also not normal to reminisce out loud about it to near-strangers; OG Sephiroth definitely seemed to already be cracking up on the way to the reactor.)
Gast was pompous and had poor judgment and less than stellar ethics, but he clearly had a self-image that wasn't compatible with being intentionally cruel; whether he was much 'better' in some absolute sense is irrelevant to the fact that Sephiroth clearly
felt he had reason to pine for him, having been abandoned to Hojo.
Of course, even if Hojo hadn't been around Sephiroth would have been raised within Shinra's corporate culture, which is still pretty toxic, but Hojo
having regular access to if not control over him as a child is one of many reasons it's easy to pity pre-Nibel Sephiroth, especially after you see more of him in CC and determine he was kind of clueless a lot of the time and not actively malicious.
(I always wish Aerith had talked a little about her childhood. She had Ifalna, of course, and having someone you know loves you even if they can't protect you much can make all the difference in the world, and then she got out while she was still a child, but Hojo had her from infancy, too. I really wish we had any of her perspective at all on...anything in her life. Other than Tseng.)
Genesis doing most of the same things Sephiroth goes on to do, to people who care about him, without being nearly as crazy, does seem to have been intended to make Sephiroth look better, especially since after Crisis Core a lot of Sephiroth's early stages of insane look like he's taken Genesis as a role model, like 'what does defying the Company for higher purpose look like? right, murder town.'
However, Sephiroth goes out of his way to be awful based on really cruddy reasoning after he snaps, and honestly it's the petty mind games as much as the actual crimes that make me utterly unsympathetic to Sephiroth-as-villain, because they show he knows
exactly what he's doing and that other people will suffer for it, and in some cases at least actively
enjoys the suffering.
And just...I'm seeing a conflation in this thread of 'feeling sorry for' and 'excusing.' You can pity without exculpating.
And as far as the debate about him needing love...honestly, that
is the impression the story gives. His fragility was definitely founded in part on isolation, and however his breakdown progressed exactly, the delusion that Jenova loved him was definitely a factor. But--and I say this with the most intense disrespect for whoever was being a misogynistic ass about fangirls further up the thread--it's not exactly the kind of isolation that's easy to break; it's not that there were no volunteers in-universe, after all. Just no one he could take seriously.
This is an arrogant, unsociable individual with immense trust issues--if Zack had been more persistently friendly over a longer period, maybe he could have made a difference, and maybe he couldn't. If Genesis hadn't been a prick, maybe he and Angeal could have. If Lucretia had come to different conclusions about which battles it made sense to fight and how safe other people were around her, maybe she could have found a way to be in his life and made the difference. Or maybe the people who think Sephiroth was the real puppet have the right of it, and there was absolutely nothing anyone could have done. Who the hell knows.
There are a ridiculous number of factors here, but without even having clarity on basic elements like 'how much psychic pressure if any was Jenova exerting on Sephiroth in Nibelheim?' we can't come to any secure conclusions.