I think the key is low time preference.

If we think long-term, we know that collaboration is more efficient than fighting.

So basically being nice is better than being rude.

You never know when you will come across a problem that the other could help you in, but he won't help, because you were rude to him.

So long-term it is preferable to be kind with everyone, because anyone might be able to help you, but you don't know who.