"Where would you like your reasoning to end?"
As is the mode in the real world, it doesn't "end."
There is an area of things that are clearly okay, a gray area of hard calls, and an area of things that are clearly not okay.
Take your dog in for a rabies shot: clearly okay.
A $5,000 operation: hard call, lots of things to think about.
A $50,000 prosthesis for a dog that lost a leg: clearly immoral.
One thing is certain: the reductio ad absurdum is often abused in our day and age. Sometimes it is valid and applicable, but often, as here, it is not.