"Stephen Hawking is a great man. He contributed immensely to our understanding of black holes."
"Socrates was a great man. Without him, we'd be missing out on invaluable philosophical insight into the nature of reality."
"Beethoven was a great man. Wow, writing beautiful music while clinically deaf! Incredible."
None of these people -- nor anyone else -- deserves to be recognized, congratulated, or praised for his efforts. Here's why:
1. In at least some cases, the "accomplishment" doesn't actually matter. For example, Neil Armstrong didn't do anything important at all by walking around on the moon; he merely served as a symbol for American "superiority" over Russia. Likewise, whoever unifies the standard model of particle physics and the theory of relativity won't have accomplished anything of importance, either, because the trivial details of our existence never, or very rarely, impact how we view what actually matters in life -- namely, our capacities for pain and pleasure, and how we derive meaning from these. Knowing the math behind what causes rocks to behave the way that they do isn't going to stop lions from tearing open baby gazelles or prevent your grandmother from suffering from bone cancer. Sorry.
2. Even where an accomplishment contributes to human progress (or Earth progress, more accurately), it was always going to happen from the beginning, as the universe's infinitude of states are predetermined by the preceding states, and are dictated by immutable physical laws. Furthermore, there is no quantifiable self inside your head, let alone one capable of making decisions; every environmental response triggered by some stimulus or another is effected by your brain long before you are even aware of what's going on. Therefore, when achieving a first for mankind, you are simply doing the will of the universe; you are not, in any way, impulsively acting on your free will.
3. Calling someone a "great man" is a stupid generalization, regardless of to whom you're referring. So Socrates was an interesting philosopher. What if he'd also beaten his kids on a regular basis (I know that he never had any; this is hypothetical)? One incredible accomplishment does not a great man make; humans are far more complicated than that, and to reduce them to singular events in their lives is to commit a grave fallacy -- whether you're vying for their greatness or forever begrudging them for solitary screw-ups.