PSA is not accusing you of altering the card; they're saying that at some point in the past, somebody altered it. This wasn't necessarily done with a malicious intent to deceive; it could have been any number of innocuous things. For example, there's the 1952 Topps Mickey Mantle on eBay that I posted a link to in the "Bearded Mickey" thread. PSA graded it "Authentic Altered" because some kid in the distant past drew/scratched a beard on Mickey. There was no intent to deceive anybody or make the card look better; quite the contrary.
https://www.ebay.com/itm/202441317919?ul_noapp=true
Or look at this T206 Cobb that PSA also graded "Authentic Altered". If you look very closely at the top border, you can see that there used to be something written in pencil there, and that somebody subsequently erased that pencil marking, also taking out some of the black border. (It's a lot easier to see if you have the card in hand and look with a magnifying glass.) I'm 99% sure that this erasure is the "alteration" that got the card its grade. Now, it's good to know about that, but I, personally, am not too bothered by it, so I'm happy to have this card in my collection. Others may disagree, and that's fine.
