As I recall, part of the rationale, was that even if there was an issue, there was literally zero way for it to be fixed. So now you spend the next 2-3 days in the shuttle, "doing your job" knowing that you will not return alive. With that in mind, the though initially was, "let's just not check".
Not true, there would've been options available. After the loss of Columbia, engineers came up with two ways to save the crew: a rescue mission, and an emergency repair EVA.
The rescue mission would've been hazardous, but the expected loss of life would have been negative. (More likely to save seven astronauts on the Columbia than to lose two astronauts on the rescue mission.) The repair would've been jury-rigged and may not have worked, but it would have been better than reentering without attempting to repair the damage.
Once you'd inspected the Shuttle, you'd know that it was in pretty bad shape. And then you've have moved into Apollo 13 mode -- how do we come up with a way to save the crew? And maybe it would've worked. It's only because the Shuttle was not inspected that NASA proceeded as though nothing were wrong.
Incidentally, they had the STS-27 astronauts check for tile damage, back in 1988. The astronauts were convinced that they were going to die on re-entry, but they still did their jobs for the rest of the mission.
This also means that NASA had 15 years to develop in-orbit repair methods before Columbia needed them. But nothing was done in this area either.
While it may have made sense in the pre-Mir days, it made none whatsoever on missions that serviced space stations. Knowing the extent of damage possible during ascent would have changed the rules by which shuttles operated.
