Comment by wavemode

This is (no offense) intellectually dishonest. Nobody wants the risk to be zero. What we want is that, if there is a specific KNOWN flaw in a life-critical system, that the flaw is addressed and the shuttle re-tested before humans are placed in it.

There's no good reason not to do this, except as a lazy cost-cutting measure (and, presumably, under time pressure to perform the eventual moon landing mission within the timeframe of Trump's presidency).