But is it actually the unmarriedness that causes the kids to go off the rails?
What if the actual cause for undisciplined kids also is a catalyst for relationships failing and crappy commitment values?
So the real issues causes bad kids and no marriage, rather than no marriage causing bad kids.
The same occurs even when you adjust for various issues and so on.
It is the lack of a stable home environment that causes the issue, and marriage is something that promotes a more stable home environment.
Fundamentally, we're reaping the failures of a badly designed welfare state, that rewards poor behaviour and excuses people from their responsibilities. Marriage, giving financial responsibility to both individuals involved towards the other one, acts as a bit more of a break against some of this behaviour.