Good people may have some bad actions squirreled away in their past. People who seem horrible now may have some wonderful actions in theirs. You never know.

"The second principle to keep in mind is that, in the Buddha’s teaching, there’s no question of a person’s “deserving” happiness or “deserving” pain. The principle of kamma is an impersonal one: that there are actions leading to pleasure and actions leading to pain. In this way, it’s not a respecter of persons; it’s purely an issue of actions and results. Good people may have some bad actions squirreled away in their past. People who seem horrible now may have some wonderful actions in theirs. You never know. The Buddha didn’t create the principle of kamma, or say that it’s good or just. He simply pointed out the way actions produce results.

So there’s no question of a person’s deserving or not deserving pleasure or pain. There’s simply the principle that actions have results and that your present experience of pleasure or pain is the combined result of past and present actions. You may have some very unskillful actions in your past, but if you learn to think and act skillfully when those actions bear fruit in the present, you don’t have to suffer.

A third principle applies to the question of whether the person who’s suffering “deserves” your compassion. Because no human being has a totally pure karmic past, if you make a person’s purity the basis for extending your compassion, there will be no one to whom you can extend it.

Some people resist the idea that, for example, children born into a warzone, suffering from brutality and starvation, are there for a karmic reason. It seems heartless, they say, to attribute these sufferings to kamma from past lives. The only heartlessness here, though, is the insistence that people are worthy of compassion only if they are innocent of any wrongdoing. Actually, people who are doing wrong are just as deserving of our compassion as those who are being wronged. There’s no need to like or admire the people for whom you feel compassion. All you have to do is wish for them to be happy. Then you do what you can to alleviate the suffering that comes from past mistakes and to stop the mistaken behavior that causes suffering now and into the future. The more you can develop this attitude toward people you know have misbehaved or are misbehaving, the more you’ll be able to trust your intentions in any situation.

The fourth principle to remember concerns the kamma you’re creating right now in reaction to other people’s pleasure and pain. If you’re resentful of somebody else’s happiness, someday when you get happy there’s going to be somebody resentful of yours. So ask yourself: Would you want that? Or if you’re hard-hearted toward somebody who’s suffering right now, someday you may face the same sort of suffering. Would you want people to be hard-hearted toward you? Always remember that your reactions are a form of kamma, so be mindful to create the kind of kamma that gives the results you’d like to see."

~ Thanissaro Bhikkhu "The Sublime Attitudes: A Study Guide on the Brahmavihāras"