Since our Catholic point of view must be against Darwin and Darwinism, why should the survival of purely material characteristics (like "white") be something desirable in the first place?
This is a fallacy. It's like saying you shouldn't worry about your genetic descendants because to do so is to accept Darwinian evolution.
This is indeed an incomparably difficult test! It is the test of Abraham with his beloved son Isaac. "Purely material characteristics" like the very beautiful white fair skin complexion of Europeans MUST be sacrificed if their cost is the high standard of our morality and religion. In fact this is the true answer to the frequent Protestant opposition against Catholic clerical celibacy: Without the sacrifice by our clergy of their would-be beloved sons of the flesh, the morals and religion of our European people can not have the Roman Catholic excellence that justifies the singular power and privilege (and beauty) of our white European race in the first place.
As Our Lord has said, only those willing to lose their life can truly gain it. Only if our race holds the perfection of God above our own human perfection can we truly achieve that human perfection, and even greater perfection than anything human. The clergy should precisely NOT "worry about your genetic descendants" and hold spiritual perfection above all else, even the greatness of temporal male descendants.
To hold the just desire for children ABOVE the desire for morality and religion is exactly the acceptance of Darwinian evolution by Roman Catholics. It is to reduce humans to the level of livestock and other animals for whom breeding is the highest achievement. But for Catholics breeding is not the highest achievement. We are NOT animals or livestock. (Breeding Catholic children is a high achievement, but not the highest one.)
What I'm saying here is that for we Catholics race is something spiritual and from above, from the Father of Lights, and not merely something material from earth-bound monkeys.
OF COURSE I want our descendants to have the beautiful white race and skin color of our European Race. In my rhetorical question in the above quote, I'm asking for the REASON why we should want to continue our skin color, not saying at all that we shouldn't want to have that skin color. But THE reason for wanting this is because that is the race and skin color of Our Lord Jesus Christ! Not only because it's a pleasant material characteristic when compared with other less pleasant material characteristics in a Darwinian lottery for better material genetic mutations than some rival group living on the other side of this or that mountain range or ocean. Darwin's envious competition may be good enough for apes and hyenas, but not for Roman Catholics.
We white European Catholics can only keep our race if we are willing to sacrifice the lesser material qualities of our race for the higher spiritual qualities of our race. For example, we must hold the Catholic education of our children above simply breeding more children. We must hold the benefit of forming a CATHOLIC military class, some of whom must die young in battle, above forming civilians who marry rather than fight against the invading hordes (especially from Russian Ghettos, and only less so from the Third World). We must truly understand that the celibacy of our genuinely Catholic clergy (now few in number) does much more for our RACE than the having many children by some of our laity. That latter option of many children probably is the second best contribution for us, but nevertheless only a distant second best even so.
It's the collectivist vocabulary used by atheists like Dr. Kevin McDonald ("the men," "the women," "the whites") that weakens our struggle for Catholic racial quality, male quality and female quality. It's more important that we raise our language to noble levels above the Darwinists and Marxists (the two are identical, of course) than that we refute them with correct intellectual arguments. The elevation of our language is worth more than the elevation of our logic.
To repeat, it would be much more productive if we use names for ourselves that emphasise moral qualities than use ones that only emphasise material qualities. "The whites" is an expression that is dangerously weak and evasive about religion and morals, whereas expressions like "white Europeans" or "Aryans" do focus on moral and spiritual qualities that can justify our devotion to our own incomparable and magnificent Indo-European white race.
Just as the Patriarch Abraham was only able to sire his own ancient white Hebrew race by being willing to sacrifice his son Isaac, so we are only going to be able to sire our future white European race if we are likewise willing to sacrifice our selves and sons -- although only for the right Catholic reasons that greatly displease the Jews, never for any apostate reasons that might please them. (The last thing that could fulfil this noble sacrifice would be to join the American or Israeli Armies!!)
I don't imagine that the white masses of Marxist/Darwinist scum are "racially superior." But OUR Catholic white folk had darned well better be.