It is such a shame that NASA learns so many design lessons the hard way. A little common sense in design and those three men would have seen old age.
I flew in the navy and Marines, the flight (NATOPS) munuals were written in blood from the accidents that occurred.
I worked with a guy on a summer job who grew up with Gus Grissom, he spoke very highly of him.
They were also in an almost pure Oxygen environment. That and the door doomed them.