Why do most people think SEO's are low life's?

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So many people equate SEO with used car salesmen or scam artists. Why does this reputation persist? There are a few "bad apples" in every field, it seems that this whole industry has been flagged as such. I personally know some great people who are SEOs and do their best everyday to help people make money and do better in search results. All SEOs cant be evil can they?