Why would one who redeems someone else's firstborn donkey be able to keep it, if he's effectively forcing the owner into a sale?

Question

Bechoros 11a rules that one may redeem someone else's firstborn donkey on their behalf. The Gemara asks: If someone were to do this, who gets to keep the donkey?

Now, there's a dispute between R' Yehudah and R' Shimon regarding whether one may derive benefit from a firstborn donkey before it's been redeemed. According to R' Shimon, who says that one may derive benefit from it, the question is invalid: the donkey is the property of its owner, and redeeming it onto a sheep does not change this. The question is according to R' Yehudah, that one may not benefit from a firstborn donkey before it's been redeemed:

להקדש מדמי ליה ורחמנא אמר ונתן הכסף וקם לו או דלמא כיון דקני להו בביני וביני לא דמי להקדש

Is it compared to Hekdesh, and the Torah says, "He will give the money and it will be to him," [i.e. to the one who redeems it]? Or maybe since he [the original owner] owns the difference [as one can redeem onto a sheep of lesser value than the donkey], it's not similar to Hekdesh?

The Gemara ultimately concludes like the latter approach; however, I'd like to try to understand the former approach.

If Shimon is able to redeem and take Reuven's donkey, effectively he's forcing Reuven into a transaction which he may not have wanted. This would seem to be a clear violation of Lo Sachmod (cf. Bava Metzi'a 5b). How could the Gemara possibly entertain that the one who redeems the donkey gets to keep it, if he's violating a Torah prohibition in the process?

Answer 1

In the "former" approach you seek to clarify, the Gemara thought that since R' Yehudah forbids the owner of a first-born donkey to benefit from its work, then that is a clear Halachic sign that the "owner" is not the owner at all. (The owner is still Hashem.)

The Torah's prohibition makes us understand that the moment the donkey is born it is in a state of "hekdesh" and is not the property of the owner.

So if the owner redeems it, then it becomes his for the first time.

Therefore, if someone else redeems it from its "hekdesh" sanctity state, then why shouldn't that person earn the donkey?

The Gemara then concludes that even according to R' Yehudah, the donkey is actually the owner's property from birth , but is merely restricted in use until a redemption takes place.

This is proven by the ruling attributed to R' Yehudah which says that someone who steals the donkey before its redemption, pays double. This proves it was always the owner's property; as one is never obligated in paying double if they stole from "hekdesh".

The reason this is not a "forced sale" like the case in Bava Metziah, is because there someone was watching over someone else's property as a deposit, and "paid" for it (without permission) and kept it. But, The deposit was always owned by the depositor.

Here, the case in theory was that the donkey was never owned by anyone. So why can't anyone off the street redeem it and keep it?

IOW, You cannot be guilty of forcing Shimon to sell you "his" donkey, if Shimon never owned the donkey in the first place!

I believe Rashi understands it this way.

See also, Birkas Shmuel , (Bava Kamma 34: 3,4) who explains it this way.

I hope this helps.