I would like to address some of his criticisms of asceticism from the "Third Essay" in the Genealogy of Morals, both to affirm some valid insights and to offer a series of counterpoints to various other insights.
The fundamental problem with the ascetic ideal as Nietzsche diagnoses it is that it has lead to a deeply unhealthy nihilism, a profound desire for nothingness, oblivion, a futile emptying of ourselves.
"We can no longer conceal from ourselves what is expressed by all that willing which has taken its direction from the ascetic ideal: this hatred of the human, and even more of the animal, and more still of the material, this horror of the senses, of reason itself, this fear of happiness and beauty, this longing to get away from all appearance, change, becoming, death, wishing, from longing itself--all this means--let us dare to grasp it--a will to nothingness, an aversion to life, a rebellion against the most fundamental presuppositions of life; but it is and remains a will! . . . And to repeat in conclusion what I said at the beginning: man would rather will nothingness than not will."
I tend to agree with Nietzsche's conclusion that a man would rather will nothingness than refrain from willing. I tend to disagree with his belief that asceticism leads to an aversion to life. In my own life, ascetical practices are precisely what allowed me to embrace life fully by tearing down the addictions that kept me wrapped up in a prison of my own whims, unable to even see the beautiful life around me.
Specifically, I find his association of the hatred of the human and material with Christian asceticism to be quite interesting. It's certainly true that there have been Christians who held views of the material world as evil, but they were declared heretics by the Catholic Church (the largest Christian church), both the Gnostics and other groups throughout Christian history such as Arius and his followers. It's certainly difficult to pin a hatred of the human and material on Christianity as a whole in light of the historical facts.
But Nietzsche doesn't stop with Christianity; he references the Buddha as well. And I think the criticism of asceticism as an aversion to life is a bit stronger with Buddhism, given that the explicit goal of the Buddha's teaching was to help people leave the cycle of death and rebirth we know as life, thereby ending suffering. That said, the Buddha chose to come back to the world and teach others, a selfless embrace of life. Also, the Buddha had studied under some of the most serious ascetics of his day and ended up engaging in some extreme self-denial in his quest for enlightenment. In the Pali canon we see that after his moment of enlightenment, he founded his practice as the Middle Way, an approach that rejected the extreme and unhealthy self-denial recommended by his former teachers in favor of a more balanced and life-affirming asceticism. While Buddhist praxis may be a search for the end of life, it is also a search for a selfless embrace of life while we are living.
Nietzsche also seems to deeply misunderstand Buddhism as a sort of nihilistic atheism, as we can see below.
"Unconditional honest atheism (and its is the only air we breathe, we more spiritual men of this age!) is therefore not the antithesis of that ideal, as it appears to be; it is rather only one of the latest phases of its evolution, one of its terminal forms and inner consequences--it is the awe-inspiring catastrophe of two thousand years of training in truthfulness that finally forbids itself the lie involved in belief in God. (The same evolutionary course in India, completely independent of ours, should prove something: the same ideal leads to the same conclusion; the decisive point is reached five centuries before the beginning of the European calendar, with Buddha; more exactly, with the Sankhya philosophy, subsequently popularized by Buddha and made into a religion.)"
The association of Buddhism with atheism is a common mistake, and Nietzsche is not an exception to this trend as he is an exception to so many others. While there was an atheistic and materialistic school of philosophy in India (the Carvaka school), the Buddhists were not it, and we can't really look to a common end for European and Indian asceticism in atheism because it just isn't there.
Should we look at the source of asceticism instead? The source of asceticism as Nietzsche described it was our sense of the meaninglessness of our existence in general and in particular the meaninglessness of our suffering.
'Apart from the ascetic ideal, man, the human animal, had no meaning so far. His existence on earth contained no goal; "why man at all?" -- was a question without an answer; the will for man and earth was lacking; behind every great human destiny there sounded as a refrain a yet greater "in vain!" This is precisely what the ascetic ideal means: that something was lacking, that man was surrounded by a fearful void--he did not know how to justify, to account for, to affirm himself; he suffered from the problem of his meaning. He also suffered otherwise, he was in the main a sickly animal: but his problem was not suffering itself, but that there was no answer to the crying question, "why do I suffer?"
This is an eloquent and moving explication of Nietzsche's view on what asceticism was meant to accomplish in the human psyche. Though I don't agree with him that asceticism is an attempt to resolve the problem of suffering by providing a meaning for it (theodicy is often used for that purpose), I do think that he is correct that human beings desperately want their suffering to mean something, for it to be purposeful.
To the extent that ascetical practices can help us build virtue, we might recognize that it is helping us to live more virtuous lives and find a meaning in our sufferings of sorts. But that meaning isn't usually enough for a human being; we so often long for a grander and more cosmic purpose with which to console ourselves, and asceticism doesn't provide that. Self-discipline and self-control as a route to the truest sort of human freedom are not very appealing as a purpose around which to build a life, particularly compared to being a child of God or attaining eternal life.
I agree with Nietzsche that the will itself is what is saved through ascetical practices. The ascetic gradually rescues the will from the clutches of transient desires and whims, from that most terrible slavery of a constant submission to the ego.
"In it, suffering was interpreted; the tremendous void seemed to have been filled; the door was closed to any kind of suicidal nihilism. This interpretation--there is no doubt of it--brought fresh suffering with it, deeper, more inward, more poisonous, more life-destructive suffering: it placed all suffering under the perspective of guilt.
But all this notwithstanding-- man was saved thereby; he possessed a meaning, he was henceforth no longer like a leaf in the wind, a plaything of nonsense--the 'sense-less'--he could now will something; no matter at first to what end, why, with what he willed: the will itself was saved."
The guilt to which he refers is not a product of asceticism; it is a product of a relationship, either with oneself or with others, which is more successful and healthy when asceticism moves the ego out of the way so that the relationship can flower. Guilt is simply a recognition that one has failed to value the relationship in the way that one ought to do so.
The notion of guilt as a source of life-destructive suffering only makes sense if one has all the maturity of a petulant child, the mewling pride of one who believes that their whims always have priority over the needs of others and relationships with others. This notion is a morality-destroying notion in human social groups.
"As the will to truth thus gains self-consciousness--there can be no doubt of that--morality will gradually perish now: this is the great spectacle in a hundred acts reserved for the next two centuries in Europe--the most terrible, most questionable, and perhaps also the most hopeful of spectacles."
This is of course precisely what Nietzsche predicts, the destruction of morality itself. Morality in general and altruistic behavior in particular are what have allowed human social groups to survive and thrive. While he asserts that the ascetic has an aversion to life, the truth of the matter is that Nietzsche is quite averse to the very ideal which allows us to live and thrive in harmony with one another. The end of the ascetic ideal would not liberate us from life-denying nihilism; it will "liberate" us from the very thing which made our survival possible.
Nietzsche is in serious denial about what makes human life beautiful and life worth living. Ironically in light of his accusations against the ascetic, he is the one in rebellion against the fundamental presuppositions of life.
Note: The above image is part of the cover of my copy of Nietzsche's collected works. See my Sources page for more information about which translation I used.