Every religion emphasizes human improvement, love, respect for others, sharing other people's suffering. On these lines every religion had more or less the same viewpoint and the same goal.
There is a common perception that compassion is, if not actually an impediment, at least irrelevant to professional life. Personally, I would argue that not only is it relevant, but that when compassion is lacking, our activities are in danger of becoming destructive. This is because when we ignore the question of the impact our actions have on others' well-being, inevitably we end up hurting them.
Criminals, people who commit crimes, usually society rejects these people. They are also part of our society. Give them some form of punishment to say they were wrong, but show them they are part of society and can change. Show them compassion.
For a practitioner of love and compassion, an enemy is one of the most important teachers. Without an enemy you cannot practice tolerance, and without tolerance you cannot build a sound basis of compassion.
Apart from selfish reasons, such as fear of punishments, fear of blame, of dishonour, etc, there remains only two motives that can stop (or prevent, "empâecher", Fr.) men from acting badly; the natural sense of commiseration (or "sympathy", - "commisération", Fr.) for one's fellow men - compassion, and the influence of education, by association of ideas ("par l'association d'idées", Fr.) - habit.
I presume that you are compassionate: to be without pity means to be sick in body and spirit. But one should have spirit in abundance, so as to be permitted to be compassionate! For your pity is detrimental to you and to everyone.
Ultimately, the reason why love and compassion bring the greatest happiness is simply that our nature cherishes them above all else. The need for love lies at the very foundation of human existence.
When something needs to be done in the world to rectify the wrongs, if one is really concerned with benefiting others, one needs to be engaged, involved. This is action out of compassion.
Nothing shocks our moral feelings so deeply as cruelty does. We can forgive every other crime, but not cruelty. The reason for this is that it is the very opposite of compassion.