Here are some heroes of ours who did some terrible stuff in their lifetime. Sure, there hearts might have been in the right place--it's pretty hard to live with your heart anywhere but in your chest--but it's interesting to know that these supposedly amazing people had some seriously devastating slip-ups due to their ignorance.
1. Mother Theresa
Here's one person that is so well known as a good person that her name is used synonymously as someone who sacrifices a lot to be kind. But, as a devout Catholic, she went around telling people not to use condoms and thus nearly created the momentum of the AIDS epidemic.
When Ghandi's first wife got sick, Ghandi had faith in God's power to heal. His dying wife begged for medication, but he refused to let her have it, saying that God would save her. As you may have guessed, she suffered through her illness and soon died. Later Ghandi got sick, and did not trust God would save him, and took the medicine.
Oprah has done quite a bit in the means of donating to nonprofits and raising awareness. However, as the new owner of Discovery Health, she doesn't appear to know anything about medicine. She promotes "alternative medicine," such as homeopathy, which is literally nothing but water, as opposed to traditional western medicine. Multiple people, including children, have died from completely preventable illnesses, who decided (or whose parents decided) to skip real medicine and go with whatever quackery Oprah is pushing.
In some senses, you could argue that these individuals are, consequentially, murderers. You could argue that they were just not critical thinkers and unintentionally abusive of their powers. Either way, hero worship is dangerous if the worshipper can't tell that everyone makes mistakes. Also, these people illustrate the dangers of ignorance, and the idea that we should reject ideas that reject reality, no matter how much we want to believe them.