未来はおまえ次第だ。

Sephiroth never enlisted into SOLDIER. He was born into it.

He was a minor when he was first sent to war. And was a minor during the majority of his time in Wutai.

He was physically and psychologically conditioned since diapers to fight and kill.

He was physically and psychologically abused.

He had no privacy and was being publicly documented since his toddler years.

He didn't go outside until his teenaged years.

He was lied to and gaslit in his desire to find his parents.

He was dehumanized.

He was turned into a sexual object by the public against his will.

He was being constantly monitored and scrutinized by an actual fascist organization that probably would have killed him if he didn't obey or failed to impress.

Whole aspects of his life were controlled and consistently regulated, to the point where he was functionally just a puppet for the organization to use and abuse at will.

Despite these factors, he still tried to be a good person. He genuinely tried. And was considering leaving even BEFORE canonically pure hearted characters like ZACK. This wasn't a former fascist having a change of heart. This was a prisoner finally gathering the courage to escape.

The irony is that he doesn't. He loses himself. He instead substitutes one prison for another in succumbing to his own hate and madness.