Our guys were killed because:
1. We were fighting evil. The Nazis and the Japanese and the North Koreans And the NVA/VC were some of the most vicious, murdering people to ever exist. Evil destroyed frees at least some of the world from them and keeps that murder from coming here.
2. We lost them because our country was unprepared for war. Our government and to a large extent, the American public, didn’t want to think about icky war and refused to fund modernization, testing, production, and fielding the weapons and equipment - which pretty much advertised to rest of the planet that we were a soft target.
Our enemies were competent, well-equipped and well led - and we weren’t ready.
Our own senior leaders were at least initially, not up to the task and wasted many good young men.
3. Not every fit young male volunteered. Many took advantage of school and various programs, or used feigned medical issues to stay away from combat. That put our best, most courageous guys into the most dangerous situations and we lost many of them.
The 4Fs, meanwhile, took advantage of the situation and bred like rabbits - which explains the large surge in LGBT adherents.
At some point, societies fail when they run out of brave young men. Substituting young women won’t help at all.
WWI made WWII necessary. But I still say, WWI was completely unneccesary and ultimately led to the downfall of Western Civilization.
What you say is true, but we have had horrific wars throughout human history, so the loss of excellent courageous men is rather continual.