It does not require any virtue to be kind to those who are kind to you. It does require virtue to be kind to those who hate you.
We rejoice when we are persecuted for our persecutors increase the intensity and value of our self-sacrifice to God. Being hated by the world for our faith is a sign that we are faithful to God and it is also a participation in the Passion of Christ. But woe to those who persecute us, for the punishment will be severe for those who persecute the faithful of God. Therefore, we must simultaneously bless those who persecute us and pray for their conversion.