Case 1: They'd done this 24 times before without problems, NASA knew all about Space Shuttle launches. Never mind what Thiokol says, they are being overly conservative.
Case 2: They disregarded procedures and disabled safety systems because they all agreed to what they were doing. Nothing could possibly go wrong.
Case 3: They had landed the Space Shuttle 50 previous times. Damage to thermal tiles was never a problem before.
Case 4: The science is settled. Don't listen to those 31,000 scientists, they are deniers. Our models are getting closer to reality, just send more research grants. Sulfur, what's that?
Consequences: Economic devastation, worldwide starvation, or worse.