I remember reading Gagarin's biography few years ago. It mentioned that testing the limits of human endurance was a part of kosmonaut's training - and that was meant literally, i.e. any mistake or problem could and did result in serious injury or death.
Similarly for their US counterparts. The astronauts were stressed in training far beyond what they'd ever encounter in real space flight. It is a miracle that there weren't more injuries or fatalities in the space program.
But in the Mercury/Vostok era, astronauts were more test subjects than they were pilots. There was very little to gain except for publicity from sending humans to space. The scientific goals could have been accomplished with animal test subjects. The role of astronauts became more involved later in the Gemini/Apollo/Soyuz era with rendez-vous, docking and EVA operations.
I'm not sure about that. There have been plenty of mistakes made by astro/cosmonaughts over the years. They are human. If "any mistake" is lethal, then we should have seen many more deaths.
I wrote about cosmonaut's training, not a trained cosmonaut's job. Those who got hurt or died in training didn't get to fly rockets. Also, that was in the Gagarin's time; after getting enough data they probably relaxed the training a bit in the next decades.
