Though this particular question does have some semblance of legitimacy, nevertheless, in its basic form, it is a misleading question of the type in which Romanists conjure up a problem to which they have a ready made solution (how convenient!) - only it's mere sleight of hand, in which the interlocutor attempts to keep his listener/reader so focused upon producing an answer that he will fail to notice the question is not even necessary in the first place. The question demands an answer - but only if the pilgrim must actually pass through that question to remain on his path.
As I said above, though circumstantially this question has some legitimacy, in its basic form it is akin to "Why don't you consider _____ (insert anything at all - the Didache, the Epistle of Barnabas, the Testament of the Twelve Patriarchs, the Apocalypse of Peter, the Epistles of Polycarp, Ignatius and Clement, John Calvin's Institutes, the Book of Mormon or the Hitchhiker's Guide to the Galaxy) the infallible and certain rule or norm of faith and practice?" The question which is far more legitimate is "Why is this our infallible rule?" We can give account for our own Canon - and this is where we ought to start to assure the hearts of our brethren. We are ourselves persuaded, chiefly, by the witness of the Holy Spirit, both to our own hearts and to the confessing church throughout history; we can rely upon the New Testament's own witness to the Old Testament canon (which it does in many ways); we can support our faltering faith with reasons both historical and textual. The question, if it is considered in its most honest form, is a question for the one claiming the Apocrypha is an additional part of our infallible rule of faith and practice - why do they so recognize it?