The mourning of which the Lord speaks is nonconformity with evil; it is a way of resisting models of behaviour that the individual is pressured to accept because “everyone does it.” The world cannot tolerate this kind of resistance; it demands conformity. It considers this mourning to be an accusation directed against the numbing of consciences. And so it is. That is why those who mourn suffer persecution for the sake of righteousness.
--Pope Benedict XVI, Jesus of Nazareth.