Buying a pet from a pet store is "saving" one life and condemning another litter to the same horrible conditions.

Supply and demand. If you buy a pet from the pet store, they will restock that puppy or kitty. They don't care if you call it "saving a life". They call it "production levels".

No demand = no supply. If we never buy a puppy or kitten, they will stop stocking animals at pet stores.