I'm not certain if it's exactly what you're looking for, but the TV Tropes site, which attempts to catalog tropes in various forms of media, calls this Then Let Me Be Evil.
Sometimes the supposed "forces of good" in a story treat an "evil" character badly enough, for long enough, that the "evil" character just gives up trying to show the heroes that they are not evil and becomes a villain for real. Prolonged exposure to the cynical side of the Sliding Scale of Idealism vs. Cynicism has conditioned this character to accept the fact that Humans Are the Real Monsters, and if they want to get anywhere in life, they have to be every bit as dirty and cruel as they are.
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In some cases, a genuinely innocent person being repeatedly framed up for committing things they never did into a stage where they have no chance to redeem themselves might as well become exactly what they are being framed as and repay their favors onto everyone.