Well, assuming they likely have some PFAS already in their system, you might just be giving them blood with the same concentration of PFAS that they already have.
Not always, as quite often the donation is on hand, but not necessarily used.
Also: better to save a life and either average down whatever PFA count they have, or bolster their blood volume so they can start producing their own lower PFA infested hemoglobin.
Lesser of evils, and kind of a win win: if everyone was blood letting for the safety and humanity of others.