J_Linebeck

Here's a guy that while (not since, and that's an important point) he was a kid had been ostracised by his peers for being way more powerful than them. Then later on it's shown that most people aren't actually aware of his power and that they respect him (Except Shinji and Kyoraku). Then when he's captain of the 5th Division, he commands respect. People look up to him, admire him, want to be around him. And what does he do with all that? He throws it away because deep down he's a pathetic loser and thinks that he's capable of changing the horrible system of lies and propaganda that the Royal Guard have exercised over Soul Society. And don't get me wrong, Aizen is absolutely justified about his goal of killing the Soul King, even the story admits that. Just that Aizen is under the extremely mistaken belief that replacing the Soul King with himself means that he'll get to change the system, whereas what would actually happen is that he would just end up being a cog in said system because he thinks that he alone knows best for everyone, and that everyone else is too stupid to think for themselves. Because ultimately destroying the figurehead of a system doesn't mean that things will automatically work themselves out. Rather, those that upheld the system from behind the scenes (The Royal Guard in this case) would simply adapt to it and maintain the status quo.

Aizen is unmistakably much more powerful than the majority of his peers especially as Captain, yet because he only believes that he can relate to others if he's as weak as them, he distances himself from them and thinks lowly of them (though amusingly he's genuinely terrified of Kenpachi Zaraki because he thinks that Kenpachi could easily kill him even if he used Kyoka Suigetsu's Complete Hypnosis). While in BLEACH: Rebirth of Souls he denies that he's plagued with loneliness and that's why he lost to Ichigo, claiming that in reality he was completely terrified of Ichigo's seemingly limitless potential, I would argue that both Ichigo and Aizen are correct.

it's that moment that really breaks Aizen down and reveals what he is. A sad, pathetic, and lonely person who can't relate to others not because of his power, but because he doesn't want to. He'd rather blame others for not being as good as him rather than admit he's just incapable of making friends. The reality is that he looks down on everyone and always would do no matter how strong or weak he was. Even if he was "just as weak" as everyone else, he wouldn't relate to them at all. All Aizen has ever done is make excuses for the way he is.

Toshiro Hitsugaya, another child prodigy, another one who was feared and ostracised at first because of how much more powerful he was compared to his peers, who also endured loneliness, who eventually became Captain and despite all that, was able to make friends and enjoy good company because he didn't believe that only equals could be friends. Hitsugaya overcame his loneliness and opened up to others, and they in turn accepted him. And Aizen can't stand that. Here is someone that was in the same boat as him, yet this person was able to prove Aizen's worldview wrong and be a decent person, someone who Aizen can't view as his equal because said person is actually better than him. It's very clear that Aizen was filled with seething jealousy towards Hitsugaya, to the point of petty targeting and attempting to tear him down constantly. That right there is a big part of why I view Aizen the way I do. He would rather lash out at everyone rather than actually try to be better. Aizen isn't someone to look up to. He's not impressive or admirable. As I said as the start, he's pathetic. He's sad. He suffers from loneliness but thinks himself above others to do anything about it. In reality he just wants to be better than everyone no matter what, and hates the idea that anyone could be given the same life as him and not be a social and emotional fuckup. That it's his fault that he is the way he is. Hell, considering how Kyoka Suigetsu's illusions in the final arc always resulted in Aizen getting horribly injured (I won't detail them here but yeah Aizen really took a beating during the fight against Yhwach) , I wouldn't be surprised if deep down Aizen really hates himself and his Zanpakto is reacting to that with by responding to a desire of self inflicted harm. Especially considering Aizen admits to Ichigo that he's no longer able to control the Complete Hypnosis ability anymore after the events of his defeat at the hands of Ichigo. It's sadly all too easy for hatred and jealousy of others to turn into self hatred, which in turn becomes a desire for self punishment over ones own failures which can lead to a subconscious need of inflicting self harm.

Now granted after the Quincy invasion he's gained quite the respect for Ichigo, and even commends the determination of humanity in a rather interesting quote:

"Yhwach, the world that you desired to create may indeed have been devoid of fear. However, in a world without the fear of death, men could not face that fear and seek out hope. Certainly, they could keep walking onward by merely living, but that would be very different from walking onward while conquering their own fears. That is why we give the act of walking onward a special name. We call it 'courage'."