The same kind of "vows" are made by marrying couples..."in sickness or health, til death do us part" but divorces happen everyday. The same kind of commitment is made when you take a job but people quit prematurely all the time, there are dozens other examples.
My point is that neither you, me or anyone who's never had kids know exactly what it's like. I don't believe people are made to be comfortable with the idea of an absolute permanent decision with no reversal. The societal trend these days if to make things even less permanent and that makes things more attractive. Think about no contract phone plans and no contract leases, people are willing to pay more for less strings.
I agree with you that before we get into any contractual or permanent situations we need to carefully evaluate and make the best decision possible and do our best to commit to it, but just because we make a commitment doesn't mean things are going to pan out and when things go totally to shit, it's hard and you can't say you know what that's like.
So before we jump on the bandwagon of throwing these parents into the dirt, think about something you've worked through on a similar level...were you able to work through it? Do you still live with it? How do you feel everyday? If you can't think of anything comparable, don't open your mouth.