Our generation has warning labels because their generation actually did it. Buncha lead addled boomers acting like we're fools for learning from their stupidity.
Taking away the instructions on how to service and repair a car was a result of capitalists wanting to make more money by forcing you to get your car repaired by them.
Adding instructions not to drink battery acid is likely for companies to avoid getting sued because people will always argue that there was no warning about drinking battery acid so the company owes you compensation.
Back in my day we drank from the hose if we got thirsty and lined up in the street to get sprayed with DDT and painted our homes with lead. Those were the days!
50ish years ago, back when people actually read Popular Science, they told people to dispose of their old motor oil by digging a small hole in your backyard, filling it with gravel, and pouring the motor oil into it.
Oh and don't forget all the advertisements for your Doctor's favorite cigarette.
Also, there are two main actual reasons why far fewer car manuals nowadays include instructions on valve adjustments:
A whole lot more modern cars use hydro-compensators, which greatly reduces the need to manually adjust the valves.
Car companies really, really want you to go to a dealership or officially certified maintenance shop so they can overcharge you on maintenance.
Sometime, you grab the manual of some old piece of junk, there's all the electronic schematics, parts list, all adjustable things that should never face end user, etc. described in it.
Now, it's just "push button. if led not go vroom vroom, call support".
To paraphrase an answer I once read: yes, we tend to introduce warnings against bad behaviours we detect and deprecate obsolete information.
In this case: I don't need to tinker a valve in an engine nowadays. The fuel injection is done through an incredibly precise system, controlled by a computer. Even mechanics require specialized tools and equipments to fiddle with that part of an engine.
Car batteries have been built more and more to be maintenance-less; you buy it, run, when it dies you replace it and that is it. Battery acid is a thing and it is dangerous, hence the attempt to divert people from messing with it.
But because less and less people are prone to go into mechanics, the need to advise against tinkering with your battery really needs to be reinforced.
Warning labels are often first written in blood before taking form of paper and ink.
Who's job is it to teach common sense? If you find the future generation lacking, that's probably your fault.
When I was a teenager, my dad gave me shit for not knowing how to change brake pads, and my response was "Who was supposed to teach me?". Like, it's not like I could afford a car working weekends, and he was always too busy to have me around whenever something went wrong. So next time he changed the brakes, he actuality taught me.
I'd make a "print a pdf" joke, but honestly, that's already an unnecessary "skill".
Sadly, technology has moved towards single finger usability and thrown out features in the process. Printing a PDF is now easy, because there's a big button (that sells you a cloud subscription for some reason), but it's also the only thing the app does.
Ah yes, when basically the only electronics in a car were the head and tail lights. I can assemble and disassemble a Willy jeep or VW Beatle by just looking at it and going with the flow, I have no fucking clue how to disassemble a modern car's door panel without breaking anything.
But if we're comparing us to boomers, let's see who's better at building a simple web scraping tool in python which runs on a raspi without any knowledge of python, Linux, AI and how to setup a raspberry pi. It took me a day to figure out.
Isn’t this more of making sure to cover all bases in case someone gets an idea of doing something dumb so they can sue? Especially in the US because it’s the most litigious country in the world.
Any time my father brings up stuff like this, I remind him that he and his brothers drove their car onto a frozen lake and almost broke through the ice, and more than once they bought tennis balls, soaked them in gasoline, and threw them at each other with welding gloves.
I know for a fact that he and his brothers did tons of dumb shit, and I won't let him forget it even if he finds it convenient when comparing generations.
So electric cars don't have valves. Oh, you didn't even think that far ahead with your boomer brain? Try to figure out why they put the warning in the manual. With all that leaded gasoline fogging up the brains, it's fair to assume grandpa drank from a battery on a dare.
Maybe the previous generation of manual writers didn't have the common sense to realize that a certain subset of people out there are stupid enough to drink the battery juice if you don't warn them not to.
Some one made the KEY comment about lawsuits. Today people sue over anything. Like you are so stupid you spill hot coffee on yourself. (coffee is hot) and then blame the people that you bought the coffee from. In earlier days simple logic was accepted and dumb people wouldn't be able to find ambulance chasers to file lawsuits for them. Today "instructions" to guide the dumber people are actually to prevent lawsuits.