I think personally it should be in a stable relationship, but that a stable home is not necessary to be honest. That being said many people cope and are very good parents and have very wise, sensible bright children other ways.

I knew a boy once who was born a heroin addict because of his mother. He was fostered by a friend and was basically my younger brother for 3 of the first 4 and a half years of his life, and then was adopted by someone else.