Obviously, you knew and served with people who lost their lives in active service. It's easy for a reader to understand that in the abstract, but the reality can be hard to imagine.
That's part of the deal; you go into harm's way when required. The flip side is, of course, that one expects that going into harm's way is necessary for good and valid reasons, and not because of some pointless activity that is just so that a politician can say that something is being done when there is no intention of doing anything.
Individuals may agree or disagree with the reasons for putting people into harm's way. Disagreement is fine. One can, for example, debate the rights and wrongs of events like the Falklands, or Gulf War 1, or Sierre Leone, or similar. The guys going into harm's way know that they're doing what they signed up to do, and that there is a perceived value to it. They'll complain about it, but they'll complain about everything, so that's no big surprise.
Where it starts to get to be problematic is when it is clear no-one actually has a clue what they're going in to harm's way to do. Take Afghanistan. It was very quickly apparent that nothing was going to change. Local allies would be given equipment, which promptly got sold on to other parties, and in due course, was used against the soldiers wondering what the point of it all was. Infrastructure, such as wells, would be dug to make villagers' lives better, only two days later, the villagers would have filled in the wells because that gave the local women too much time to gossip.
But I guess what really annoys is when one reads tosh about how easy a certain campaign (and the Falklands is a good example) was, and how "only" a couple of hundred of British boys died. It's only a small number, and it's very easy for people to forget that even a small number can have family consequences.