Q. Why are the martyrs of the Holocaust called k’doshim?
They are contrasted with the angels, who are also called k’doshim (e.g. Psalm 89:8, Zech. 14:5, etc.), and God Himself, who is K’dosh Yisra’el, “the Holy One of Israel”, a common phrase in Isaiah. The martyrs show their holiness ba’aretz, by the way they live (and in this case, die) on earth.
K’doshim do not always die for their faith. They live by it. Their principle is kiddush hachayyim, “Sanctification of Living”. They live holy lives by never abandoning their faith or abdicating their Jewish dignity. They would prefer not to have to die for it, but if there is no choice they will die nobly and win a moral victory.
One thing they will not do is to allow themselves a murderous spree in which they rake the world with death and pollute the earth with blood. K’doshim are not paragons of perfection, but despite their imperfections they are heroes of the spirit.
Such certainly were the k’doshim of the Sho’ah.