Oh boy, here we go. I just made another 6 paragraph dissertation. :s Buckle up.
I'm not sure if you're just young, or very naive.
War is hell and has ALWAYS been hell. Innocents have ALWAYS been caught in the crossfire and always will. It's just that prior to more modern communication, it's been harder to see and it used to be easier to just think of the enemy as "the other, inhuman, so it's ok if they die". You think that medieval wars were honorably fought? Hell no. The only time war was even REMOTELY civilized was when the british lined up two columns of troops against each other and had them fire off a bunch of rounds and whoever had the least casualties won. Which didn't last long before their opponents decided "Fuck the rules, if I take cover behind this tree and pop off shots between their shots, I'll kill them all and not get killed!".
War is never really "just" or "noble" because there's ALWAYS an aggressor. Yes, as the defender, or someone who jumps into help the defenders, there's justice and nobility involved. But someone always has to START the damn war to begin with. And to do that is almost always done for incredibly selfish reasons.
There's rarely an "honorable" reason to start a war which will kill thousands or more of your own people and your opponent's people. Because all it does is beget more death.
And it's not like returning to "human element" warfare will help any. Do you know what happens when you have boots on the ground? Best case, some Soldiers get jumpy and see the enemy everywhere and will shoot innocents by accident at some point. Worst case? "Burn, Rape and Pillage"
Also, it's not like going back to a "mix" is even possible. The only nations that can fight in that manner are the bigger nations and superpowers. Which are either in a large tangled web of alliances which means one declaration of war leads to a World War, or it means that the forces in conflict have access to nukes in case they lose. That and no one wants to send thousands to millions of their own citizens into a deadly meat grinder conflict when there are more efficient and less bloody (for your side) ways to fight. I mean, seriously if someone's coming at you about 40 paces away with a knife, are you going to prefer to fight him with a knife of your own, or pull out a shotgun and kill him before he risks killing you? Most people will choose to not take the risk and use the safer option.
...That and the nations with less military power (Say...The various terror groups?) aren't going to want to fight a VASTLY superior army man-to-man on the open field. They know they have a better chance of winning or at least staying alive longer if they use guerilla tactics and human shields. Like, we have the Geneva conventions for a reason. But does it stop ISIS or whoever from openly flaunting them? NO! They don't give a shit about not being dicks, they know they're unable to win in a way that's not shitty, so they fight shitty so they can stand some small chance to win!
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Now, I'd ask WHY you want to return to a "mix" so there can be fighting for honorable causes, but I already know the answer. "Competition"
Competition is WIRED into all our DNA. It's why we've all survived this long. And the purest form of competition is conflict. Combat. This is what makes us regard combat as "honorable". It's what attracts all of us to the idea of Combat and War.
Hell, I'm 90% a pacifist and even I have fun playing violent games, and have fantasies of how much criminal ass I'd kick if I had superpowers, and stuff of that nature. It's wired into all of us in a primal way.
But here's the thing. War isn't honorable. It's never "Clean". It's always because someone who has the power to order around the protectors of the nation (the military) to do their bidding and they want something. No rational person goes "I want to fight an honorable war" and just does it for the hell of it, because they know their people and likely them will die.
And even if we replaced actual War with a simulation or sports game or paintball or competitive chess between the leaders of the nations or some other kind of nonlethal conflict, do you REALLY think that a nation who stands a physical chance of winning will submit to a loss on the field of "pretend" battle? Or do you realize it's more likely they might go "Well, fuck this fake war, then. I know we can win this in ACTUAL battle, so if you wanna take your win, come and fucking take it from our cold dead hands *commence land war*"?
Like, imagine if tomorrow some tiny little nation said "We challenge the USA to war, which will be fought as Full Contact Rugby, the loser has to surrender half their land" and the US somehow accepted, and lost, do you REALLY think that the US would follow the terms? Or would they go "You want it, come and take it by force"?
You want honorable conflict? Play a sport. Get into MMA or boxing. Play competitive videogames. Go sign up for Lacrosse (Fun fact, Lacrosse is sometimes called "War's Little Brother").
Or hell, go do paintball (I can confirm it's REALLY fun, and cemented in my mind FIRMLY that while I enjoyed the experience, I NEVER want to join the military. It's scary having "bullets" fly right past your head when you know one hit = you're "Dead")
Real war is hell. Innocent people die. Soldiers die pointlessly. The only time it's ever justified is if someone attacks you first. Which makes THEM the bad guys for starting it. At least unless the defenders do something unforgivable and vicious in response.