This really gets lost in the traditional nuclear family argument. From personal experience, having both biological parents in the same house doesn't mean a healthy family environment, and no amount of moralizing is going to wish it into being.
Also overlooked is the impact one can have through simple acts of support and empowerment.
Had a High School teacher that let me into a photojournalism class that was already full (the school admins denied my schedule transfer after we had moved to the 'correct' side of the street (literally) and into an upper middle class school district). This teacher simply allowed me to be socially-weird-awkward-me and set a basic structure to thrive in (eventually winning state and national awards with the school newspaper). By giving me (and others) a chance to show we belonged and could compete helped build my self-esteem after it had been consistently torn down at home.
Didn't know it then, and doubt that teacher has any idea, but it changed the course of my life. I think I'm more a practical realist or even a cynic about life and society than I am optimistic - still, that experience reminds me to try and build others up and pay that empowerment forward