Societies would _not_ be better off if everyone were like Mr Spock, all rationality and no emotion. Instead, a balance - a teaming up of the internal rivals - is optimal for brains.... Some balance of the emotional and rational systems is needed, and that balance may already be optimized by natural selection in human brains.
Incognito: The Secret Lives of The Brain (ed. Canongate Books, 2011) - ISBN: 9780857860477