I mean we literally get Henry saying that he could've fought back if he wanted to but he didn't at any point
he says this, with tears running down his eyes, also the ENTIRE point of why he's terrified of his cave memories and why it brings him anguish is because he killed a man, and was then controlled by an entity, and that entity buried the memory of it, and even the idea of it haunts him, if he were inherently evil, the cave memories would mean nothing to him, its not traumatic as it would just be the start of his great "becoming".
the entire plot of the series involving him as "Vecna" is that he targets kids because they are malleable and controllable, they can be broken easier, which is made ironic as he was done just that, even the speech Cop Dad gives to Eleven can be directed at him, but unlike Eleven, Henry didn't have friends or a Cop dad and simply had given in to the evil in his head from the Flayer.
And no, the Flayer is not dead, that was just another physical body made for it, the FLayer is the black mist shit, it needs psychics to give it form and coherent thought to channel through, through Henry, it forges a body made out of the Demogorgon's and shit native to that world to inhabit but it itself is bodiless, this is why its essence makes kids that have psychic potential gain psychic powers, out of necessity because they are needed for it to be true physical threat, its not a big ass Spider, that's just Henry's shaping of it.
No one's going to feel bad for Henry because he did awful shit and none of them have any idea the context of why he became that way, except Will, and in the end, it doesn't matter, Henry submits to the Mindflayer, you can say he did it willingly, but its very obvious to me, he did it because he felt he had nothing else and believed he was as evil as it made him, ain't no Cop dad to give him Eggo Waffles when he was 12.
