I would disown him/her since they have insulted the Church and Myself. I will also be worried for the sakes of the soul of my apostate child (Since Apostasy is an excommunicatable Latæ Sententiæ offense in the Catholic Church) Though this is my opinion right now but it may change years down the road.
If that child wants to be an apostate, then that child is no son/daugher of mine. That apostate child would just be another heathen who has tossed his salvation away.
I too will chime as a person who is depressed, and to a significant extent disgusted by this attitude. A religion is a deeply personal matter for someone to make decisions about, and it is the height of arrogance for a parent to force a child into a religion. A person has to consider what they truly believe, and you have no right as a parent to force a child to accept your beliefs. You can introduce the child to them, teach the child about them, but you have no right to insist the child accepts them. (It is incidentally for this reason that I place no value whatever on infant baptism. This is a sop to the parent's faith, not the child's, since the child has no input or ability to register its beliefs).
(Though I was resistant at the time when my parents tried to force me into a church when I was an agnostic and not ready).
So why is it any different that someone should be forced into Chistian habits that they have no belief in? An agnostic meaninglessly (and resentfully) going through the motions of Christianity at a parent's behest would seem more offensive to God in my opinion than someone who withdraws from such ceremonies completely.
I dont see it as fair that parents have to disown their children, but if they need to be stern about their children following their faith, then they should disown them if the child wont conform to the family's religion.
To force someone to "conform" to the family's religion if they have no genuine beliefs in it is a despicable act, and would be regarded as such by any morally superior being. An empty and resentful charade of a religion is far worse than none at all.
Everyone has to take their own path on their religious beliefs, and that is not always going to match that of their parents. You yourself admit you went through an agnostic phase where you resisted your parents efforts to conform you to their faith, and yet you seem to feel it is your duty to repeat their error. I would not attempt to force any child of mine to adopt my religious beliefs, and would certainly not disown them for adopting an atheist or agnostic path. One thing I would consider disowning a child for though would be if they had the unspeakable arrogance to insist that not only are their beliefs the only right ones, but that they have the right and indeed duty to force those beliefs onto others.
I actualy dont find it disturbing that people "force their children" into religion. Its an obligation that many married Catholic Couples (as well as married Catholic+non-Catholic couples) have that they should raise their children to be Catholic, they make a promise to the Church to raise their children to be Catholic. Who says that I am right? Mainly I believe that the Catholic Church is a true religion.
You have the right to believe whatever you like about the Catholic religion. You have the right to
teach your children about it. You do not have the right to
indoctrinate (there is a very fine distinction here) or
force a child into the Catholic church.
There is also the final point I come back to. An agnostic has not even denied the existence of a God, and yet you feel they are an apostate (deliberately perjorative term) heathen who will burn in hell for all eternity (If you like I'll explain why no being of acceptable morality could decide to burn someone in hell for all eternity, especially for their beliefs). To quote a certain game that quotes a certain person "I do not feel obliged to believe that the same God who endowed us with intellect and wisdom intended us to forgo their use". For true belief of any kind a religion must be considered deeply, and if that requires an agnostic, or even an atheist phase I see no reason why a God should object. Someone who has carefully looked at their faith, and discarded all those aspects which are morally objectionable or of no real meaning I would think would be counted as a far truer worshipper than some 'yesman' who merely accepts what their parents tell them is right. Also if someone feels that what humans have made Christianity into is not the appropriate religion to follow, why should they follow it? Only your own arrogance in asserting that you are the only true religion. I personally would think that any God worthy of such worship would put little score on ceremony, and only place value on true beliefs. The formalities of the Catholic Church, religious ceremony, and and similar human trivia is of less than no value without true belief, and in my humble opinion of little value even with it.
And there you have in detail why your attitude disgusts me, and why I think it would disgust even the God of the Catholic Church you are so intent on forcing your child into, at least if that being is of such moral excellence as to be worthy of the worship you insist your child gives Him.