Hyehudi.org has decried several times the total subversion of Judaism via numerous worthless fictions, including the upcoming travesty of “selling” Chametz on Erev Pesach. Although there seem to be several ancient valid legal fictions (Ha’arama), these do make sense in context, and /or cannot be unduly extended further.
One less ancient example is the custom of “selling” a mortally ill child to someone else. The idea, beyond arousing his guardians’ repentance, is that if his true parents’ actions made them culpable to lose a child, God forbid, the child in question would cease to be a legitimate target, and recover from his illness.
I have come across the claim this historical fact is a support for the validity of Jewish legal fictions in general. After all, the transaction (Kinyan) ought to be invalidated on grounds of obvious insincerity. Neither the buyer nor the seller has any intention of passing ownership: דברים שבלבו ובלב כל אדם. If legal fictions are wicked and Jewishly ineffective, how come Torah scholars and rabbis never protested?!
Firstly, without over-explaining, legal fictions ‘work’ fine in metaphysics, properly understood (don’t ask). In any case, a Jewish child does not legally belong to his father. More significantly, there is no religious aspect here. Even if the sale is but dark humor, neither Judaism nor Hashem are being mocked thereby. (This custom is not, in fact, uniquely Jewish.)
Note: Biblical “Pidyon Haben” consists of a symbolic monetary fine for release from sacrificial duty, not passing ownership.