We're supposed to, you know. We're supposed to hate the sin and love the sinner, and pray for our enemies. We are to pray that the evil receive the grace of faith and are redeemed. The great saints prayed for those who persecuted and killed them. Christ prayed for those who were killing him, and asked that God forgive them. We are to imitate Christ.
Now this doesn't mean that I spend time on my knees praying for Michael Jackson, as I have bunches of other people to pray for. But we shouldn't rule out praying that dictators, killers, child molestors, etc. see the Light.
It’s about 2 weeks too late to pray for Michael Jackson.