I agree with Dianne: not every evil person is happy.
But at times it does seem that those who have no concern for human life or for the rights of others, etc., prosper. And we see many who are responsible, caring persons struggling with afflictions (illness, financial hardship, injustice and other issues). That's why David's Psalm talks about it.
On the other hand,only God knows the motives and true intentions of our heart and what drives each of us to act the way we do. We are not capable of judging them correctly and that is not our calling.
I agree with Eagle: I do feel sad that people die without ever knowing or experiencing love. God loves each person and regardless of their wrongdoings, I believe we should respect life. He is the giver of life. Each day he gives us is an opportunity to choose to live for Him or choose to live selfishly for our own purposes.