then why are such households more of a a hotbed of domestic violence, alcoholism, drugs, infidelity and confused, unhappy children than those of married couples?
Are they? I can think of a few families which meet those descriptions and which are married. I can also think of a few families where the father just ran like a hae and left the single mother to raise the kid... and they are very happy, well-balanced, loved kids.
Of course, there are well known examples of loving familes in modern times; long term and married: