Why be nice when you can can get the same by being cruel

[gaelic cowboy]

Strictly theologically. Works better, being liked doesn't pay the bills. Even in moderation we aren't that nice, school and work can be hell. So what is it that sets us apart. Being nice (and if you aren't)

If you lived in a poorer region of the world like say Borneo or some place in Africa you might not have such opinions.

We have a concept in Ireland called Meitheal

Meitheal (Irish pronunciation: [ˈmɛhəl]) is the Irish word for a work team, gang, or party and denotes the co-operative labour system in rural Ireland where groups of neighbours help each other in turn with farming work, such as harvesting crops.[1] Neighbours who give their work to others are helped in turn with their own heavy seasonal tasks so the heart of the concept is community unity through cooperative work and mutually reciprocal support. Meitheal is the Irish expression of the ancient and universal appliance of cooperation to social need.
The term is used in various writings of Irish language authors. It can convey the idea of community spirit in which neighbours respond to each other's needs. In modern use, for example, a meitheal could be a party of neighbours and friends invited to help decorate a house in exchange for food and drink, or in scouting, where volunteer campsite wardens maintain campsites around Ireland.

Despite the poverty and there obvious hard life those people in Africa etc help other people all the time.