I’ll use your statement in the place of what would have been the first part of my response, but still give the caveat I was going to give.
We do also have a responsibilty to our health, as I believe some extremely ascetical saints expressed towards the end of their lives (St. Francis, as I recall, asked the forgiveness of “brother mule the body” for the harsh treatment he had put him through).
In light of our understanding today of infectious disease, drinking the puss of the sick would be an extremely bad idea, and would have been even more dangerous in an age before antibiotics.
Saints who did such a thing did so either out of ignorance of the danger, or if they did realize the danger (people did have some sense of contagious disease even before germ theory explained it) then they did a wrong thing out of good motives. I doubt any of them were were truly, blitheringly insane, especially those whom the Church has explicitly set before us as models of heroic virtue through official canonization. It does not sound as though they drank puss because they thought it was tasty, or disfigured their faces while not realizing what they were doing. They knew quite well the natural horribleness of what they were doing, and did it anyway as an intentional deprivation for the sake of God.
G.K. Chesterton described the ascetical instinct as a natural human instinct, one which like other instincts must be kept within a healthy moderation. I think he was right, not because asceticism is an animal instinct like the drive for food, sex, comfort, etc., but because human beings are naturally a compound being of body and spirit, and the spirit feels freed by overcoming the animal instincts of the body. However, this impulse, despite being fundamentally good like all our natural impulses, can like the others be taken too far. Chesterton’s example of this is the unhealthy extreme asceticism of Hindu India, in which people put hooks in their backs and pull them, and all sorts of other nasty things. Christian spirituality, being incarnational in nature, has an inherent tendency towards moderation of the ascetical impulse, without by any means extinguishing it entirely. I think St. Theresa of Avila is an example of a saint who began by undertaking extreme mortifications, then eventually came to a more healthy balance.
In our increasingly hedonistic and health-obsessed world, our cultural conditioning is generally in the opposite direction, towards creature comforts and against bodily mortification. Viewing past ages through the lens of modern Western culture, their ascetical practices can at first strike us as horrible. If they had been able to see forward to our time, they might have seen us as lazy and worldly and ungenerous toward God. The right attitude might be somewhere in between, not quite as cautious as most modern Catholics but not quite as extreme as some of the saints of old.
Finally, to round out the discussion, I don’t know the accuracy but I heard once about a reported discourse between one of the Desert Fathers and a young disciple. The disciple asked something like “Abba, in the last days, will the Christians fast like we do and hold vigils like we do?” and the Desert Father answered something like “No, my son, in the last days men will hardly have the strength to fast for a single day or keep vigil for a single night. Yet they shall be greater than us. For we contend with the devil chained, but they shall contend with the devil unchained.”