You make valid points. However, you're fighting against years of social conditioning ever since the girl was wearing diapers and you'll be fighting an uphill battle, even if the woman is wife material.
In fact, I would argue it creates a stable family unit because most women view marriage = security. Plausible deniability you are not going leave her. You and I know that a relationship can end anytime, married or not.
Its a tall order to get a woman to have kids out of wedlock unless you are a top 0.0001% male. Even as a 1% male, if you want all the benefits without a legalized marriage, some other 1% dude will.
And let's be realistic here, very very very few men will be able to pull it off.