Dissimilar redundancy only provides safety if you are willing to use it by disabling the option that proves unsafe. The decision to put a crew on Starliner show

Dissimilar redundancy only provides safety if you are willing to use it by disabling the option that proves unsafe. The decision to put a crew on Starliner shows that NASA has completely missed the point of contracting multiple providers for ISS access. Columbia killed people because NASA saw the flaking foam but kept flying the shuttle because they didn't have another option for space access. Afterwards, Commercial Crew was written up with multiple providers to keep this from happening again. Imagine an alternative timeline where NASA learned that relying on one launcher was dangerous 20 years earlier from Challenger. In that world, apparently NASA would see the foam issues and still sent up a crew on Columbia's last flight to preserve 'dissimilar redundancy.' Nevermind that this was a policy instituted _specifically_ to make it politically easy to ground unsafe vehicles. Utter insanity.