Not true - for the most part social media and the other types of ads, etc you mention are about reinforcing already-held beliefs, or otherwise giving them direc

Not true - for the most part social media and the other types of ads, etc you mention are about reinforcing already-held beliefs, or otherwise giving them direction. Persuasion is about actually changing someone's mind. This is why a given political ad can reinforce the beliefs of two people who believe opposing ideas: One says "See, I KNEW it was true." and the other says "See! I knew the media/platform/community was biased this way!"