Shuttle launches and re-entry are strenuous situations for the vehicle. "Wear and tear" (including some loss of tiles) has occurred on each and every launch and is expected.
Jael's post DOES refer to "wear and tear" on flight STS-87 (December 23, l997) that was greater than previously experienced. (It also makes passing mention of similar, albeit lesser, damage that occurred on the previous flight, STS-86.)
In comparison, the tragedy we experienced with Columbia was flight STS-107.
Rather than becoming frantic over a single report of "wear and tear" suffered 20 flights ago, I'd be more interested in seeing a tabulation of the comparable inspections that occurred with the intervening 20 flights. It would have been with the benefit of that additional experience that the experts would have been basing their judgement whether any potential damage caused by the foam at liftoff was within "normally" acceptable wear & tear parameters.
"Wear and tear" is one thing and yes, a certain amount of tile loss is normal but I was under the impression that this chunk of insulation colliding with the wing at Mach2+ was an unusual event.
We will just have to agree to disagree on this. I say it was something that should have been checked out to the greatest extent possible rather than subjected to speculative risk analysis. The stakes were too high.
Actually, the report is much more sinister than a simple wear and tear issue. The guy in charge of inspecting these parts of the Shuttle makes that clear that this was a huge amount and that the amounts had been increasing. (Since the Freon-less formula had been used.)