Why do trolls even exist?

Trolls are people that we could all live without in this world. All trolls do is ruin lives and make people feel bad about themselves for stuff that they do not need to feel bad about. I have never understood why people would want to hurt others so much, because how is that fun? I know personally, I could never hurt someone intentionally on the internet, or in person to the point where they may delete their social media accounts. I feel like trolls have insecurities and issues in their lives, so they ruin other people's lives in order to feel better about their own. That is so bad however, because people deserve to have a life without ridicule. You never know what people are going through in their lives, and for trolls to still put down people like they do, it is sick. It is especially sick when someone has a death in the family and trolls target that, like when Zelda Williams was attacked by trolls after the death of her father. It is terrible that someone would be so heartless that they would attack her on twitter like many trolls did. That is not funny whatsoever, and it is not appealing at all. If someone thinks that making people feel bad and depressed is funny, they need to think again. Trolls are so disrespectful that I honestly wonder how they go about life knowing they are slowly crushing people's minds. Trolls are using their right to free speech, but they should still know better than to make people feel sad and depressed when they do not need to feel that way. I wish trolls could be stopped, but everyone does have the right to say what they want, so unfortunately we will be stuck with them for a while longer.