Re: "Just look at how the Challenger disaster happened"
The cold O-rings might have been the direct cause of the shuttle exploding, it wasn't the cause of the accident. The roots of what allowed the accident to happen and the reason the decision to launch was made lie deep within the culture and organisation of NASA at the time. Read the entire accident rapport (and especially Feynmans Appendix F of such) and read between the lines. Yes, many people were aware of the dangers and many were aware of the possible ways in which their "bit" of the shuttle could fail. Nobody really had a good overview of how all these complex systems worked together and how things could cascade. Likewise, foam shedding was never really linked to thermal protection system damage, and thermal protection system damage had never properly been investigated.
NASA tried multiple times to get different shuttle designs worked out but got stonewalled because they "HAD a shuttle". And the STS itself formed a VERY poor basis for further development as it had been painted into a very difficult corner by the demands placed on it by the military (mainly: once around orbits requiring large cross-range capability and thus large wings, high cargo capacity thus requiring a very large oversize cargo-bay, the decision to use "reusable" engines that turned out to be so complex they weren't actually cheaper than just dumping them in the ocean but made the vehicle much heavier and much more complex)