Warning: long winding rant to follow.
Friendly fire deaths were certainly under-represented before Vietnam. Up to that point, we were much more jingoistic in our fighting--Huns/Krauts/Japs/Gooks killed our men, we didn't. Anything that disagreed with that storyline was almost certainly whitewashed.
The real story is not the rise in killing of US troops by friendly fire. It's the overall decline in killing of US soldiers by the enemy, for several reasons. Our government has much less of a stomach for getting our own US soldiers killed since Vietnam. No president wants to hear chanting like, "Hey hey LBJ, how many kids did you kill today?" So we have better armor, better weapons, better training, and we do more of our fighting with missiles/drones/mercenaries/locals. And we're much better at saving our own wounded. But the ferocity of our weapons sometimes leave less margin for error. To simplify, if you are wearing body armor and throwing hand grenades from air planes and the enemy has rocks and pointy sticks, the biggest danger is often that the grenade blows up in your face.
Check out this interesting chart about
US soldier mortality by war. It's fascinating to note that nearly half of all deaths occurred in the Civil War, the ultimate "friendly fire" war. 625,000 dead. Compare that to the longest-running war in US history--Afghanistan has a "meager" (if you don't happen to be one of them) 1,135 deaths.
Since Vietnam, less than 12,000 soldiers have died for our country. Vietnam alone had 58,000 killed.
On one hand, that's great for our country because nobody wants to see American soldiers die. But I think there is a flip side. The generation that fought in WWII was the "greatest generation" because they truly understood sacrifice. They knew that if you voted for war, a lot of people die. Maybe not our own people, but a lot. So George Bush Sr. didn't fuck around with war.
That generation also knew nothing was easy. If you wanted to put a man on the moon or pay for old people's health care or build a highway system or beat the commies, you had to pay taxes for it. They also saw first hand through things like the GI Bill that government spending worked when used properly, but you couldn't go overboard or you'd end up like the USSR, imploding under the weight of its untenable economy.
I look around and I see a nation of buffoons and charlatans, offering quick fixes and demagoguery.
I see China make 25 year moon shot commitments to electric cars and infrastructure, while we make 25 year moonshot commitments to Afghanistan. We're getting our asses kicked, and we're so unlike the Greatest Generation that we can't even be bothered to look up from our iPhones to notice.
Nothing makes a person, or a country, more serious about things than when it notices it stands a pretty damned good chance of dying. In our video game bailout nation, death leads to a respawn or a handout. A spiraling deficit leads to a tax cut or a new program. Nobody is seriously worried about working together to fix the problems, because the last generation to really be forced to do that are in their 80's and too worried about their Medicare.
I don't know if I should be happy or depressed that our nation has had it so good for so long.
tl/dr version: Friendly fire seems bad because we're getting killed less by the enemy in wars. That has made us a nation of pussy whiners.
