Historically, around 60% of all astronauts were from the military which is a high-risk occupation.

In the 50s, there was something like a handful of test pilots dying every single month. A subset of the ones who survived became the first astronauts. My understanding is that there are still a significant number of astronauts who were test pilots first.

If you don't have massive risk tolerance, you don't sign up for a moon mission.

Each and every one of them is fully aware that it’s a massive risk and has made their peace with that. You’re getting strapped to a giant rocket. It’s inherently dangerous

Is jumping on a grenade to save another person suicidal? Or is it just a matter of you not agreeing with the rational?

...no? It's the same as when you say you'd 'die for somebody'. I don't want to die, but if I had to die to save my family I would. That's not being suicidal. Similarly, if space is important enough to you to take this risk (which realistically is a pretty low risk!) I wouldn't call that suicidal either. I take the risk of death driving in my car every day; that's the nature of life.