If you spread goodwill to people you don't like, they pick up on the fact that you don’t mean them harm. That protects you from a lot of dangers outside, because they don’t want to retaliate.

"A lot of people out there are really hard to like. In fact though, it’s especially important that you spread goodwill to people you don’t like. It’s a kind of protection. You make up your mind that you don’t want to harm them, you don’t want anybody to meet with any harm.

Part of that, of course, means that you have to treat them well, but also it means that they have to learn how to act well, too. This is why you can spread goodwill even to people who are cruel and have done a lot of evil in the world. You hope that they see the error of their ways and change, because that’s what’s going to lead to their true happiness. You want them to understand the causes for true happiness and be able to act on them. And you want the same for yourself.

This way when you go out into the world, you’re in a much safer place. On the one hand, other people pick up on the fact that you don’t mean them harm. That protects you from a lot of dangers outside, because they don’t want to retaliate. But secondly, and more importantly, it protects you from yourself. If you have some unskillful attitudes or intentions toward other people, you’re going to create a lot of bad karma. That karma’s going to come back at you. So it’s in your own self-interest to have goodwill for everybody.

It may not come easily, but then you can work through it person by person. Is there anybody out there for whom you have no goodwill? There probably is. Then ask yourself why. Why would you have ill will for somebody? You don’t benefit; they don’t benefit. They’re going to retaliate. Goodwill means that you hope they understand the causes for true happiness and have the strength to act on them: that they have both the understanding and the strength.

If there’s anything you can do to help, you’re happy to help. If not, then at the very least you hope they find their way, but you don’t pose any danger to them.

In having this attitude, as I said, you don’t pose any danger to yourself. After all, when you have this attitude of goodwill, why would you say something unskillful? Why would you think something unskillful? Why would you act on motivations that are unskillful? You don’t want to see anybody harmed. And particularly you don’t want to harm yourself.

As the Buddha said, the people who harm themselves are the ones who break the precepts. When people mistreat other people, the harm comes back to them, sometimes manyfold."

~ Thanissaro Bhikkhu "The Perfection of Goodwill"