Traditional Buddhist teachings tell us that we should love all beings because -- over the course of many lifetimes -- everyone has been your mother in one of them. In traditional Buddhist southeast Asian cultures, this is a valid metaphor for creating an attitude of love, respect, and gratitude for all beings.
Here in the west, that ain't necessarily so. Our relationships with our mothers are fraught with tension. We rebel against them, seek to separate from them, blame them for our messed-up psyches. So if you tell a westerner that all beings have been their mother, instead of unlocking a well of love and respect you might find the thought, "So that's why they're so hard to get along with."