We have a 14 year-old son presently in confirmation classes (and a 16 year-old who went through it a few years back). I would never dream of making this optional, at his age (i.e., for frivolous teenager-type reasons: it's "boring" or "uncool" too time-consuming, and suchlike). My opinion is, "this is what Catholic teenagers do, as fundamental in the process of faith formation. And so my teenage children will do it (assuming that they accept the faith), and have no choice in the matter.
That is something I would view as responsible Catholic parenthood. The choices of one's children are restricted, in the nature of things. They don't have unlimited freedom. Sometimes they think foolish what is actually best for them. The parent is -- oftentimes -- in the position to know better what is best for the child than the child does. And so we (when necessary) make them do things they don't like or even may think are "stupid." Making confirmation optional denies, among other things, the communal, covenantal nature of the Body of Christ.
On the other hand, we ought to -- by all means - answer the child's questions, and ought to cultivate a healthy inquisitiveness and curiosity about spiritual matters (hopefully, confirmation classes do this themselves, which should be part of their essential purpose). If we can't answer, then we need to figure out how to locate resources and persons who can do so. The obligatory nature of confirmation for a non-adult doesn't preclude open discussion and inquiry about theological things.
Now, remember I am presupposing a Catholic child who accepts the teaching of the Catholic faith but just doesn't want to attend because it is inconvenient or unnecessary or some "typically teenager" response. If it is a matter of actually disbelieving something, then it would be a more complex "conscience issue" and it'd be almost self-defeating to force someone to go through a thing that is supposed to be voluntary and indicative of a personal desire to go forward in the spiritual life.
Of course, with teenagers, these things can be very fine lines, and what seems to them to be unfair compulsion might seem to the parent to be merely a necessary stepping-stone to adulthood and/or spiritual / character / social formation, etc. They often confuse necessary and unnecessary things.
But (with this factor in mind), what about compulsory Mass attendance? Isn't this largely the same situation as with confirmation? God and the Church want Mass attendance also to be heartfelt and voluntary, and not a mere drudgery or coerced activity. Vatican II stresses our personal, whole-person involvement in the liturgy. We are supposed to be actively worshiping, not just sitting there passively taking things in.
If a compulsory confirmation class / ceremony is rejected based on the freedom of conscience and the nature of confirmation, then would it not follow that compulsory Mass attendance for someone who doesn't want to go would possibly fall under the same opinion? Yet we know missing Mass deliberately is a mortal sin. In any event, if we as parents "make" our children go to Mass, there may be cases where they really don't want to go.
I'm just thinking out loud. Blessedly, I haven't had the problem about Mass with my kids, They seem to enjoy going, or if not "enjoy", at least to recognize its inherent importance and to act with appropriate reverence (though my 6 year-old daughter fidgets an awful lot in church and threatens to go to sleep about every week!).