I struggle to make sense of the implication that Catholics are nihilists (even in some narrow sense).
* Nietzsche saw nihilism as revelling in nothingness, but also as coming in a preferable version which was simply about iconoclasm and modernization.
* He saw Christianity as having a purpose of underpinning objective knowledge, thus opposing nihilism, but as failing in this, due to the erosion of belief and rise of skepticism.
I don't know if you're making a point specific to Catholicism, maybe. Can't work out what.
Christianity is life-denying, world-denying. Nietzsche concluded that christian ethics lead to life-denying societies.
Foundational to christianity is the belief that this world in which we find ourselves is a temporary punishment, and that this life only has meaning to the extent that we use our time to endure suffering and restrict ourselves. If we do this, we will then be rewarded with an actual life, an eternity of having the pleasure to watch our enemies suffer.
Another foundational belief is that all humans are born defective, and as a consequence the ideal is to never procreate. The most devout christians live in gender segregated communes and (officially) never engage in sexual activity. What could be more life-denying and nihilistic?
Personally I also find the solution to this original debt, this ever-present defect, highly suspicious. That is, that it needs to be repayed through human sacrifice, and then we all need to partake in this sacrifice through symbolic or actual cannibalism.
So, yes, Nietzsche saw in this a 'will to nothingness', a categorical denial of the possibility of a meaningful life and even a denial of life itself. He found it interesting, however. Compared to the ancient greeks he as a philologist knew quite a bit about he found the christians and the power dynamics they introduce devious and in some regards more sophisticated. 'You might be dominating me now, but you just wait, when Christ returns he will put you to eternal torment and I'll be watching, wallowing in the pleasure I derive from your suffering' is rather devious, both as a psychological power play and as an ethos for society at large.
From how you're describing MacIntyre he seems to have been mostly preoccupied with defending a dying academic epistemology and not really have engaged with the text of Nietzsche.
In medieval Christianity there were stylites dwelling up their pillars and (some thousand years later) anchorites sealed in their cells, and all this stuff about life-denying rings true except that Catholics, in the modern era at least, are mostly pro-life and anti-contraception and breed like rabbits.
MacIntyre wrote a book called "After Virtue" which is mostly posing Nietzsche against Aristotle, and his late-life conversion to Catholicism was because of Thomas Aquinas, who was an Aristotle fanboy. I don't know how he squared this with the supposed virtues of asceticism and living for the next world.
Religion gets into philosophy far too much, and kind of makes a big mess, since it doesn't have to make sense.
Well, catholics, like most christians, consider it worse to have sex for pleasure (or otherwise satisfy desire and gain intense pleasure) than bring more sinners into the world. Celibacy is still the ideal and roman catholics have a long list of rules regarding who can have sex and under what conditions.
You might have noticed that christians have a long history of negative attitudes towards men who have sex with men, i.e. performing sexual acts for pleasure alone, as it is understood. Women don't feel pleasure from sex so lesbians have gathered less christian attention, and it's the penis that does the insertion of the homunculus and so on, hence it's the actually sexual thing involved.
From the Wikipedia page about After Virtue I get the impression that MacIntyre mainly engaged with Nietzsche through secondary sources. For one I have trouble reading the geneaology as promoting greek morals rather than using them for contrast, and I'll have to agree with Nietzsche that the labour movement, the main egalitarian movement of his time, is unlikely to birth a new kind of person that rises from the carcass of the old morality and initiates a new. If such a person comes it is likely that they will be perceived as elitist or aristocratic.
As for complaining about Nietzsche being non-egalitarian, that's rich coming from a christian thinker, who believes this world exists merely to separate the good from the bad so that the good can have some bad ones to gloat at for eternity.
And yes, historically, to a religion it's philosophy that is the main threat, since philosophers don't create martyrs, they create dissidents, unlike nasty emperors and the like. Things have changed since then, however. Under the nihilism of modernity the main problem for a christian theologian has changed from the non-believer to the non-person, to paraphrase Rick Roderick (who got it from a colleague in theology, I think).
I might have to read After Virtue to figure out whether MacIntyre addresses this, since if it's in there the wikipedians didn't mention it. I kind of doubt it though, if he did he wouldn't have put so much faith in projecting his ideals regarding purpose onto other people since he would have realised that this practice was already in service of capital accumulation.
* Nietzsche saw nihilism as revelling in nothingness, but also as coming in a preferable version which was simply about iconoclasm and modernization.
* He saw Christianity as having a purpose of underpinning objective knowledge, thus opposing nihilism, but as failing in this, due to the erosion of belief and rise of skepticism.
I don't know if you're making a point specific to Catholicism, maybe. Can't work out what.