Or at least the more memorable ones seem to have that tragic edge. I've just been listening to "The Reaping" (with the 6th Doctor) and "The Gathering" (with the 5th), but it's true of "Spare Parts" (the Genesis of the Cybermen with the 5th Doc) and even "The Girl Who Never Was". What is it about Cybermen? Daleks are easy to hate, being creatures of hatred themselves, simple-minded exterminators of everything "inferior". Cybermen are something else. It's not just the mere fact of turning people into cyborgs that's the problem. What's wrong with people getting artificial limbs, say, or an artificial heart? Most people, unless they completely reject technology, would have no objections to saving or enhancing lives with it. Even completely artificial lifeforms (robots and AIs and so forth) can be perfectly humane, even in the Doctor Who universe. But somewhere along the way, the Cybermen lose their "souls". I think it's the urge to "perfection" that kills them. They think they're perfect, they're immortal, and that they can make the universe perfect. They're people, ordinary people, good people, who have suffered so much pain that they want to get rid of pain forever. They've been crushed by the unfairness of life.
This makes "Spare Parts" difficult for me to listen to. I mean, I watch Doctor Who to escape from our depressing reality, but the Doctor can't save Mondas. In the end, he can't do anything at all for the people there. They're doomed. It's not fair, but they're doomed. All he can do is watch.
The new TV series is missing something in their alt-Cybermen stories. They're more like humanoid Dalek knock-offs. "Delete!" indeed. Pfeh.
But it's something to think about when creating your monsters. Doctor Who sometimes really nails it. (Let's not dwell on their failures.)