Peony raises some questions about filial piety to which I would like to respond.

I agree that a child's relationship to his or her parents is a fundamental building block of Confucian ethics.  Indeed, I think Confucius is a genius in this: he is constructing a moral theory on a relationship that, for many, many people, is the most emotionally powerful human connection they have.   Of course most parents (though not all) love their children with a certain depth and intensity, ferocity even.  And, in experiencing that love, most children (though not all) will want to reciprocate that love.   How humanely commonsensical, then, to begin with this relationship as a primary ethical obligation of care, and then move out to other relationships.

But an interesting problem arises when we confront conflicting obligations.  Does Confucianism require that we always and under any circumstances privilege our obligations to parents over all others?  I think not.

I know that, historically, filial piety has been given a certain primacy, both culturally and legally, in East Asian contexts.  But that historical experience is not the only possible expression of Confucian morality.

To get at the possibilities, let's go to Mencius and the story of Shun, the mythic sage-king.

Shun was said to be reverently filial,
even though his father, who had tried to kill him on at least two
occasions, was evil and deranged. When young, Shun knew he had to get
married because to have no spouse would be the worst offense against his
parents. But he also realized that his father, in all his depravity,
would not allow any marriage to take place. To do the right thing by
his parents he would have to defy them. What to do? Shun secretly wed
and did not tell his parents. He disobeyed and deceived them to secure
the greater good of extending his family relationships, and thus, Humanity, in the world.

Now, you'll notice that I am not invoking the creation of a male heir as the only justification of marriage as a filial duty.  First, I see nothing in Confucian thought, at least from the Analects or Mencius, that requires a male heir for the fulfillment of filial duty (again, historical experience notwithstanding).  Daughters can honor ancestors and care for parents as well as sons – indeed, I believe daughters carry out theses duties, generally, better than sons. Second, it is not at all clear to me, despite historical experience, that birthing a child through marriage is absolutely necessary for the realization of Confucian Humanity in the world.  Various alternatives exist: adoption is fine; helping other children, unrelated by birth, could pass along the memory of one's ancestors; etc.  I will concede that, for Confucians, having children, male of female heirs, is a uniquely good way of extending Humanity in the world, but, I would contend, it is not the only way to do so.

In any event, what did Mencius say when he argued that Shun was right to disobey his parents and get married?  Let's go to the text (9.2 or 5A.2, depending on your dispensation):

Why did Shun marry without telling his parents?

Because [said Mencius] he would not have been allowed to marry if he had told them.  A man and a woman living together is the most important of human relationships.  If he had told his parents, he would have to put aside the most important of human relationships, and this would result in bitterness against his parents.  This is why he did not tell them. ( Lau translation)

"The most important of human relationships."  Wow, that's big.  Their is no mention of an heir here, but we can reasonably assume that, given the context of the time, it was assumed that having an heir was what defined the husband and wife tie as "the most important of human relationships."  But we have some wiggle room here for modern sensibilities.  At the very least this whole situation suggests that Mencius, and I would argue Confucius also, was not rigidly dogmatic in their approach to weighing and judging parental versus spousal obligations.  Sometimes to be a good spouse, one has to disobey parents.

I am aware that, in section 8.30 (4B.30), that Mencius says one of the five ways to be unfilial is to be overly attentive to one's spouse, at the expense of parents.  But if we consider this in connection to Shun's filial disobedience, I think what we have is a range of possibilities.  Mencius is telling us to take our obligations to parents very seriously.  But we must also highly value our spousal obligations.  The primacy of one over the other is not automatic.  It depends on context and circumstances.  At times, we must do what is necessary to fulfill "the most important of human relationships," and at other times we must obey our parents.

Bottom line: I think it is justifiable, as a modern application of Confucianism, to speak of our duties to cultivate our "closest loving relationships."  That is, there are duties beyond filial piety, however important our obligations to parents are.  And, indeed, not all of us can be Shun-like in our filiality.  If our parents are not enacting their duties to us, their children, then that may weigh in the balance as we consider what the right thing to do is in any particular circumstance.  Mencius recognized that most us will, at times, have reason to be resentful of our parents: 

This does not get us off the hook morally.  But it does suggest that parents are not always right. And we should tell them so, when they are wrong:

In serving your mother and father,
admonish them gently. If they understand, and yet choose not to follow
your advice, deepen your reverence without losing faith. And however
exhausting this may be, avoid resentment. (Analects 4.18)

We can disagree with our parents.  We just have to do so in a respectful manner.

At the end of the day, then, yes, a child has a powerful prima facie obligation to obey, and to care for, parents.  But that is not the only obligation an individual has.  And how that duty is performed will depend upon a careful and conscientious calculation of how other obligations -  to spouses, to children, to other "close loving relationships" – are affected.  Remember what Confucius said when asked about his greatest ambition:

To comfort the old, to trust my friends, and to cherish the young" (5.26)

He didn't mention his parents….