My problem with this is that NASA's attitude seems to be "nothing we can do, so we won't look to close at the potential problem in the hope that'll just go away."
I suspect a good everyday analogy would be a moderately thin peice of concrete, although something more akin to styrofoam might be more appropriate. It has low sheer strength, and thus if you drop it, it's going break. Put it on top of something else, and in compression it's pretty strong.
Still the tiles are fragile enough, even when on the shuttle, that they restrict flight through rain when transporting the shuttle piggyback on the modified 747. (OTOH they might be worried about ice or hail imbedded in the rain). It's possible that the debris was ice, but for some reason they thought it was the foam, and that would make a big difference. Unless the foam is pretty brittle, which it might be, I can't imagine what one normally thinks of as "foam", pulverizing that way when it hit the wing. However, think of the stuff you can buy in a spray can to fill cracks around your house, that stuff is really brittle and crumbly when it dries. The new insulation is a spray on, so it might indeed be pretty brittle.
Somehow I think the focus on the debris hitting the wing during the ascent will turn out to be a dead end, and the actual cause of the crash something else entirely, but I'm not even sure myself why I think that.
OTOH, they probably did look at the debris "problem" and decided that it wasn't a problem after all and so did not require the sort of effort that they otherwise would have put in place as soon as they discovered it.