Whether it's "goodness", naiveté, or simply ignorance, in the end it's the result of cognitive dissonance - they've built a worldview where such perversion/evil doesn't exist (or is contained or warded by "good") so explaining to them their worldview is flawed takes a lot of effort that they will resist changing. Even those who seek to change find it difficult.

Many people for whom factual truth is anathema to their self-esteem.