My take on it, from various reading, is that there were three major reasons why launching was a bad idea...
(1) Significant presence of ice on the spacecraft and surrounding launch structure, with unknown effects.
(2) The known problems with the O-rings at low temperatures, which had been under investigation at Morton Thiokol for about 7 months. It's well documented that the engineers at MT had made it clear that the launch "go" should not be issued, and that they were overruled by politically minded management in that company.
(3) That in the Atlantic, in the booster recovery area, the two recovery ships were in an "Extreme survival condition", and completely incapable of doing anything beyond stay upright(ish) in 50-70kn winds, 100ft seas, and routinely 30° pitch attitude changes.
The reasons these were ultimately disregarded are much debated - but clearly the desire to prove that they could launch the Challenger *at-all*, the high profile nature of the mission with Christa MacAuliffe on board, and increasing presidential scrutiny were clearly all in the mix. It seems highly unlikely that it was any one single factor.
My interest in the wind-shear / B757 issue is mainly that if reported to NASA it would have been *another* reason to cancel. However, I suspect strongly that it probably never was.
G