It would satisfy their sense of defiance to be told: "Of course you'll b****y well go to hell you omadhaun" but, of course, none of us are able to fathom the extent of God's forgiveness and so it is not reasonable to present a response in that manner.
However, the catechism is unequivocal in stating that, a) missing Mass deliberately on a Sunday is a mortal sin and b) anyone in a state of mortal sin will consign themselves to hell. Therefore, if you defy the teachings of Christ and commit a mortal sin you are like one of the millions of snowflakes that are destined to everlasting agonies, as witnessed by St Theresa of Avila.
We know, do we not, that it is legitimate to hate sin because it breaks our link to Almighty God and also to hate it because it has the capacity to send us to eternal fire. Of the two the former is by far the better stance to take but, I have to admit that fear of hell and Satan have always held a particular horror for me and, as a result, I have always opted to endeavour to avoid sin in order to avoid hell, most unsuccessfully I hasten to add.
This is not the best route to take; love of Christ should be our main thrust but..... human frailty and all that.
The choice has been crystal clear to me since I was a small child and I really cannot understand Catholics (CINOs) who apparently cannot see the outcome to 'no Mass on Sundays'.
Try hard to behave and to keep God's law and you may make it to Heaven where we shall no longer experience the fears and sorrows of earth but will be happy beyond our wildest imaginations or......break God's laws and suffer the endless and hideous torments of hell that are so awful they are beyond description (although many of the saints and those who have witnessed visions of Our Lady have captured the essence of that nightmare place pretty well).
Here is Sister Lucia's terrifying account of her own vision as permitted by Our Lady:
"The rays of light seemed to penetrate the earth, and we saw as it were a sea of fire. Plunged in this fire were demons and souls in human form, like transparent burning embers, all blackened or burnished bronze, floating about in the conflagration, now raised into the air by the flames that issued from within themselves together with great clouds of smoke, now falling back on every side like sparks in huge fires, without weight or equilibrium, amid shrieks and groans of pain and despair, which horrified us and made us tremble with fear. (It must have been this sight which caused me to cry out, as people say they heard me). The demons could be distinguished by their terrifying and repellent likeness to frightful and unknown animals, black and transparent like burning coals".
Hmm.....I know which road I shall be continuing down; after all, it seems such a piddling price to pay....go to Mass on Sundays and Holydays of Obligation, love God and love your neighbour and you get your stay out of jail card!
Remember too the words of Our Lady of Fatima after she had shown the vision of hell to Sr Lucia.....
To prevent this, I shall come to ask for the consecration of Russia to My Immaculate Heart, and the Communion of Reparation on the First Saturdays. If My requests are heeded, Russia will be converted and there will be peace; if not, she will spread her errors throughout the world, causing wars and persecutions of the Church. The good will be martyred, the Holy Father will have much to suffer, various nations will be annihilated. In the end, My Immaculate Heart will triumph. The Holy Father will consecrate Russia to Me, and she will be converted, and a period of peace will be granted to the world. In Portugal, the dogma of the Faith will always be preserved. Do not tell this to anybody. Francisco, yes, you may tell him.