Why can't they let me be?

Because you are more awesome than them and that really doesn't make them happy. always remember, if your actions and your beliefs answer to your conscience then there is nothing wrong in them. and conversely, if your conscience doesn't sanction something, there's nothing right about it .

Because they think making people sad and annoyed will make them feel better, and they feel it will help them and it doesn't...

that's just people. they comment and they annoy you. a lot of people in this world think they know better than you. and gossips are intriguing. not all though.. some people aren't like this

Let's assume in this scenario that "They" are bullies or trolls. They harass you but for some reason, even though they dislike you, they won't leave you alone. What do you do in distressing scenarios like these? Ignore them! They feed off of your attention and reactions, if they don't get any of that from you they will get bored and move along.

You really can't please everyone. I have always been the type of person that likes to live up to people's expectations. In that way, I thought they would love me more. And they did. But I ended up losing my ass. And as horrible as it is, one false move that I made and they stabbed me right in the back for being wrong or for thinking that I was right. Here's the lesson - no matter what you do, wrong or right, there will always be people who will go against you. Don't retaliate, though. You just can't control their thoughts, and neither do they have the power to control you. So don't let them.

because everyone has different opinions of everything. even about what each individual person should be

Because no one let them be themselves. People try to force their opinions on everyone else, it's the way they are brought up. A lot of people lack empathy, they lack thinkign capacity and simple don't want to listen. It's not your fault. It's not their fault either. Everyone have their own problems. Some are given by others, some they create themselves. Everyone have their own perspective, and most people don't even try to look things from others perspective either. Just like you don't wan them to force you for anything, they dont' like being forced either.