Was Space Shuttle safe enough for human crews?

Space Shuttle was a compromised design from the beginning. They originally wanted the Space Shuttle booster to also have wings and return to launch site (with a crew!). But they couldn't afford to develop two new vehicles, so they compromised by making the external tank as cheap as possible and adding solid rockets (which led to the Challenger disaster).

But their biggest mistake was having the engines on the orbiter (so they could be recovered) but not the fuel tank. That meant the orbiter had to hang on the side of the external tank, which made it vulnerable to foam strikes (leading to the Columbia disaster).

Landing with wings is aesthetically pleasing (compared to tower catches) but consider the waste: You have to boost the weight of the wings, landing gear, etc. all the way to orbit and then bring it all the way back. It's much more efficient to just bring fuel and use that for landing. And if your guidance is accurate enough, a pinpoint landing means you can land on the launch tower and not worry about landing legs.