Supreme good is like water. Water greatly benefits all things, without conflict. It flows through places that people loathe. Thereby it is close to the Way.
When we speak of a calm state of mind or peace of mind, we shouldn't confuse that with an insensitive state of apathy. Having a calm or peaceful state of mind doesn't mean being spaced out or completely empty. Peace of mind or a calm state of mind is rooted in affection and compassion and is sensitive and responsive to others.
Humanity is not without answers or solutions regarding how to liberate itself from scenarios that invariably end with mass exterminations. Tools such as compassion, trust, empathy, love, and ethical discernment are already in our possession. The next sensible step would be to use them.
'Thou shalt not kill' does not apply to murder of one's own kind only, but to all living beings and this commandment was inscribed in the human breast long before it was proclaimed from Sinai.
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.
If pity was always equally alive and acting in all individuals and in all circumstances, we could do away with moral. Unfortunately, it is not compassion, but rather it's contrary, selfishness, that act most strongly in us.
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.
If you resort to violent methods because the other side has destroyed your monastery, for example, you then have lost not only your monastery, but also your special Buddhist practices of detachment, love, and compassion.