Museums should lock up the paintings in glass boxes with locks on them, maybe. Hanging them on the walls seems like a bad idea for a variety of reasons. What about climate control for example? Don't paintings need specific conditions to keep them from fading over the centuries? I saw the how the Shroud of Turin is displayed, on TV once. It's behind so many layers of bullet-proof glass and whatnot that one day when the building it was in caught on fire and it needed to be removed, it took a small army of people with sledgehammers quite a long time to get it out. How it's displayed, you can still see the thing, through the glass and whatnot, but it's safe, and a 6-year-old can't walk up and walk away with it.