All a dogma is, is a doctrine that is defined ex cathedra and binds us to believe.
All a doctrine is, is a belief that the faithful have always believed and Church has always taught. A dogma cannot be a "new doctrine" (which is another term for heresy) or something that is new. V1 tells us: "For the holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine." So this is how we would know true or false if he ever went to define a dogma, but the whole idea is merely a speculative exercise in futility because with faith, we know this can never happen.   
 

You just exposed yourself as being totally disingenuous. Stubborn, remember that it’s reprehensible to lie, but what’s worse is to lie to yourself.

Thank you for this link. Here is an extract from the concluding pages 133 and 134:

"All we can do is to conclude practically with St. Bonaventure, that it would be a most incredible and most horrible thing to doubt of the true beatitude of any one whom the Church has canonized ; with Melchior Canus, that a man who did so would be temerarious, impudent, and irreligious ; with Benedict XIV. that he would be rash, give scandal to the Church, dishonour the Saints, favour the heretics who deny the authority of the church in canonization, and would himself savour of heresy, as preparing the way for infidels to deride the faithful ; that that man would be an asserter of an erroneous opinion, and obnoxious to the heaviest penalties, who should dare to affirm that the sovereign pontiff had erred in this or that canonization, or that this or that Saint canonized by him was not to be reverenced with the cultus dulis ; and, finally, with the Dominican Billuart, that whosoever should deny that any one canonized by the Church was a Saint and in glory would not certainly be a formal heretic, but would be, first, temerarious, because he would contradict the common opinion of the Church in a matter excellently well founded, and whose opposite has no adequate foundation ; it is the most insolent madness, says St. Augustine, to dispute whether that ought to be done which the whole Church does ; secondly, scandalous, as drawing the faithful away from the cultus of the Saints ; thirdly, impious, as insulting and dishonouring the Church and her Saints "

The bold type is mine.

Why should anyone therefore deny the saintliness of John Paul II ?

Again, all you have to do is put yourself in any fallen away Catholic's position who wants to repent of their sins of heresy. Imagining this is typically something very simple to do - fyi.

Yes, of course. A Catholic who commits any mortal sin, no matter what the sin, always can (and should) go to confession and receive absolution.

But, according to Pius XII, the sin of heresy severs a person from the Body of the Church.  It is unlike any other grave sin (except schism and apostasy):

23. Nor must one imagine that the Body of the Church, just because it bears the name of Christ, is made up during the days of its earthly pilgrimage only of members conspicuous for their holiness, or that it consists only of those whom God has predestined to eternal happiness. It is owing to the Savior's infinite mercy that place is allowed in His Mystical Body here below for those whom, of old, He did not exclude from the banquet.[20] For not every sin, however grave it may be, is such as of its own nature to sever a man from the Body of the Church, as does schism or heresy or apostasy. Men may lose charity and divine grace through sin, thus becoming incapable of supernatural merit, and yet not be deprived of all life if they hold fast to faith and Christian hope, and if, illumined from above, they are spurred on by the interior promptings of the Holy Spirit to salutary fear and are moved to prayer and penance for their sins. - Mystici Corporis Christi

What you're saying is that PPXII is saying once a heretic, always a heretic? That the confessional is forever closed to repentant Catholics guilty of the sin of heresy? But note what he says in the next sentence. 

Again, if tomorrow *you* chose to defect from the faith and joined the Lutherans as a woman priest, and after 10 years came to your senses and wanted to repent, what would be the first, or at least one of the first things you would need to do? You would need to walk into the confessional as you always used to do and confess your sins to the priest, only Catholics can do this.