Here be the speeches!
I'm less convinced of the bleeding of video game morality into real-life, though it's plausible,
With those who came to gaming as adults I'd be less worried about, as their personalities are well established, so any change would be minor and take a long time and be tempered by dealing with the real world with existing habits. But even then, it can have an effect over time, for which some will be more susceptible than others.
Of course, it's kinda creepy when a 40 year old tells you he likes rpgs because it allows him kill and that the only reason he doesn't kill in the real world is because it is socially unacceptable and would lead to others sticking him in prison or killing him in exchange, a reason notably lacking any moral consideration. It shows what he is inside, an immoral murderous a-hole who is luckily too cowardly to ignore social standards.
Kids are much more vulnerable though. Kids can quite literally have their memories retroactively altered (there often special rules police have to follow in questioning kids because asking questions in the wrong way can shape their testimony), that's how malleable they are. And problem solving is a skill that applies to both games and the real world, so if kids are establishing their habits for problem solving in a very unrealistic game environment, then that will carry over into the real world. This is actually why I think rpgs can be great teaching tools, because you can instill good habits and let kids try things that generally result in death without permanent harm, of course, if it results in death in the real world, then obviously it should in the game as well, otherwise kids might get the wrong idea. You just have to be careful of what you're teaching.
Still, it is worth considering, for variety if nothing else. Having enemies act like people who want to survive amd have reasons for doing what they're doing, and npcs punishing immoral behavior would be a change of pace worth exploring even if everything I said above was 100% false.
I also wonder how widespread or new the behavior of people simply killing whatever they encounter to finish the encounter and rack up XP.
There has always been a split in the community. Gygax even complained about how some people would play the rules and completely miss the game itself.
Computer games near universally play the rules.
You can figure out some things by looking at the game's design however.
Consider gold=xp. This mechanic meant you merely needed to grab the loot to get the xp, and that was in the days of when combat was dangerous. Players would naturally be encouraged to avoid fighting.
On the other hand though, many hated the gold=xp because it didn't make sense to them that picking up a gold coin would make you more skilled. (This is of course the wrong way of thinking about it. The gold coin can only be gained by navigating the "dungeon" and therefore the xp is for everything you went through to acquire the coin, and agnostic to the methods used.) Thus many would house rule different ways of gaining xp, commonly altered to combat. This eventually became the norm and thus found it's way into the offical game.
The Dead Alewives' "I cast magic missile on the darkness" skit is from 1996, so it's not a new phenomenon.
'96 is about 3 decades after the game came out, so it's not exactly the original either. Consider also the current age of those who grew up in the '90s, and the impact people of that age are having on the world now. Still, even in the '90s it was not ubiquitous. You could easily find groups and even computer games that avoided such. Yet consider the last 20 years and how things changed. Now it is a challenge to find a group that would have a thought, much less a problem, with the wholesale slaughter of characters that are merely labeled enemies.
This has become pervasive, and video games are even worse most of the time with counter examples being few, and that's the environment the activists and college age kids have grown up in, and look at how different the morals are. Environment has a lot to do with that.
Then there's the logic of organized play, which is probably many new players' first experience with the most popular TTRPGs. In my experience, those modules very much favor an approach of checking off boxes to maximize return on XP, though they're a bit more complex than "kill anything that moves."
Organized play is probably the whole reason the popular style of play is often considered the correct way, if not the only way, to play by most.
Organized play is also set up to be easy to monetize. Companies make a ton of money from selling APs and modules and what can be called "content." Way more than from mere mechanics and even tools. However, that makes them want give a consistent experience regardless of the gm, and that means writing for a narrow set of outcomes and expectations. Organized play is like the fast food of rpgs, and as such will always be more popular. However, having a well-cooked healthy fancy restaurant or home-cooked meal is wonderful and often more satisfying. My major disappointment on this front is all the players who think fast-food is the only good food and can't even recognize a fancy dinner as edible much less worthwhile.