Quoted from Tranquilize:
"Destroy" was your word choice. My previously routed 20 year old w/b machines look great. Are they scratched and dented? YES! Does anyone without the perfect angle of lighting and a keen eye for anything that is not factory direct perfection notice? Hell no! Protectors are just silly. That is just my opinion. You have every right to attempt to keep your playfields pristine, but your attempts defy a lot of what the physics and manufacturing of pinball machines are all about. The games are meant to wear, and even cheap-assed sterns wear well.
I mainly got them, because I have a lot of crap to do. (just like everyone else). If I'm not able to get to clean a playfield as soon as I'd like on location, then it's piece of mind that the protector is the thing that's going to take the brunt of the force and not the playfield. Will the playfield still dimple to some degree.. yeah, maybe. not why I got them though.
I plan on having a lot of these in my rotation for while and anything I can do to prevent more work later is a plus in my book. Don't think anyone ever said anything about no wear what's so ever.. all they were meant for is preventing it, just like mylar or cliffy's.
If someone at home wants to add one I'm not sure why everyone is saying they are a bad or silly idea, it an assurance. It's not affecting you and if you get a game with one and it bugs you, they take literally 5 minutes to cut out.
Bottom line is until we see a playfield after 10 years of being under a protector, I don't think anyone can really judge with 100% certainty either way.