Alex, I’m not sure…
Alex,
I’m not sure the drowning-rescue case is the best hypothetical for the principle you want to prod me on, because the loss inflicted on the owner of the life-preserver is likely to be nearly zero, and the owner is unlikely to demand any compensation for it. Even if she does, it would be unjust of her to demand a level of compensation that’s disproportionate to the trifling loss imposed by taking the life-preserver. But here goes, anyway.
On my view taking the life-preserver entails taking on a debt to the owner of the life-preserver. As with any debt, you need not be able to repay the debt in full immediately; you just need to be willing to make a good-faith effort at repaying it as quickly as you can. Presumably the stranger that you saved from drowning might also chip in for the compensation—although whether she can be compelled to do so may depend on whether she was aware that you took the life-preserver without permission from the owner. In the case of something as trifling as taking a life-preserver that’s not otherwise in use,
Now, if you realistically expect that you and the drowning stranger together will still never be able to repay a substantial amount of the debt to the owner, then I suppose it would be wrong to take the whatever you’re taking, but I can’t imagine how that would come up in the drowning-rescue case. But in those other cases it may not be so obvious that it’s permissible to take the more precious property without permission.
In any case, I think that if you’re not willing to accept a financial burden, if necessary, as the cost of saving someone from drowning, then what you’re doing doesn’t deserve the name of virtue.