I beg to differ here, we do marry in the way Allah prescribe to us, also it is Sunnah. But we are still marrying for our own sake, and has the right to choose the best possible person suits us.
I agree with you on obligation of help strengthen the spouse's faith. But end of the day everyone is answerable to his/her own deeds to Allah.
Everyone is accountable for their own deeds. And there are those who will be held accountable for the deeds of others. Like a parent would for his child's upbringing, or a husband who neglected his wife's lack of piety.
Marriage is something that Allah (SWT) made lawful for us. If you marry because you just want to and not to please Allah (SWT), than the blessings won't be there.