Why is it so hard to be nice?

I've always been taught that nothing beats kindness. I'm always as kind as I can be, which can be hard sometimes. I know that if someone is angry at you it doesn't help to return that anger. Instead, you should stay calm and be nice and act like a reasonable person. So far that has helped me a lot. Whenever I stay calm and kind in nasty situations I feel much better and stronger, simply because I know nothing can beat kindness. If I say kind when someone is angry at me, I will always win. If I give in to anger then it will only get worse and the situation might go out of control. Maybe I explained it a little weird, but it's how I feel.

I never understood why people feel the need to be mean to each other. I mean, if you see someone on the street whose hair you don't like, is yelling something mean at them gonna make you feel better? Why do people find it fun to hurt someone else's feelings? What do you gain from that?
This is just something I simply cannot comprehend.`

I'm not saying that I'm a perfect angel who never means harm, but at least I'm not mean to others. In fact, I can't be. Just the thought that I insulted someone or made them sad makes me feel so terrible that I just cannot bring myself to do or say something mean to someone. That doesn't mean I can't say anything mean to someone about someone else, but I will never say it straight to their face because why would I hurt that person? Besides, I'm never the one who starts with being mean. If I say something mean about someone to someone else it's always because they did something similar.
It's honestly not that hard to keep that mean comment to yourself. And if you really want to get it off your chest, say it to someone who is not the person in question. It can save someone's day.

But that's just a start of what this post is about. I haven't even talked about bullying, homophobia, transphobia, racism, and all those kind of things.

Why do people make it their mission to ruin someone's life by bullying them? Why do they put so much time and effort in making someone else feel terrible? What is wrong with them?

Why do people hate LGBT+ people? Because the bible said so? You know how many other things the bible forbids? I doubt those people listen to that too. Gay people are people, trans people are people, we are all people. We are people with thoughts and emotions and opinions and we are all valid.

Why do people hate on poc? They have done nothing wrong, but just because they have a dark skin they are getting harassed and killed. Wake up people! You're being ridiculous!

Why is it so damn hard to be nice to each other? Why can't we accept each other for who we are? No matter the colour of your skin, no matter your sexual orientation, gender identity, or religion. We're all living beings who deserve respect and acceptance. Why is that so hard to understand..?