Yes you are a savage. Putting it back where you found it is not the correct way to do things. It might have been in the 1970s, I don't know when cart corrals first showed up because people were too lazy to take it back to the front of the store.
I don't think they put it back where they found it. It's not worded well but I'm pretty sure they put it up (aka "returns") in the property place when they're done with it.
It doesn't make you an animal or a savage, it makes you at best willfully ignorant.
If your mother taught you that 2+2=3 but later in life ample evidence shows you that 2+2=4, do you change you mind or still insist that your mother knew best?
Your mother's mindset regarding the returning of carts is called "lowest common denominator", someone else doing something wrong doesn't make it OK for you to do.