He’s guilty over something that wasn’t his fault, the death of his people. His violence sprouts from that need to save, the need to be in control. We can easily imagine a younger Thanos having a less dangerous need to control. When tragedy struck, this need for control manifested as an obsessive quest to control the population in the universe.
His unconscious fantasies of control are shown in his view of most of The Avengers as children. After experiencing the trauma, Thanos has seen the very real effects of violence. Thanos had to face that violence upfront, and to him justifies exacting violence on the universe.
In justifying his actions, Thanos views himself as a god, pointing out society’s flaws, which just happens to involve not killing half their own population. In being the hero….the god, Thanos wants his will to be enforced with the snap of a finger. He feels he has that authority, that he alone can kill half the universal population.
Thanos also believes he has the authority to blame the victims who are “in the way” of him achieving his goal. He blames them for things that are unrelated to his own violent actions, similar to his own self-blaming. Thanos also seems to be willing to face any challenge at any point, seemingly unbeatable. This “perpetual agitation” makes him truly formidable, but tied together with his victim-blaming, points me in another direction.
Thanos’ masculinity is toxic, frustrated,
His desire to control others can’t be easily changed, but his willingness to kill half of a population must be changed. Thanos expresses his traumatic life through toxic masculinity, and we get genocide on a universe-wide scale. In his smirk of victory in the face of a sunset, Thanos’ violent subjectivity is finally at peace, for now.