There's also another sub-text here, "School is a sham, and so are adults." Adults in anime, when they are not missing, are usually either a joke, or villains. The teacher who speaks of her miserable love-life, the police officers who think of glory, are corrupt and/or just fail to subdue the enemies. These are obviously so our heroes could step in, but at some point the message is damaging, in how it paints all adults as something to be ignored or outright defeated. The adults who foisted these arbitrary and ill-fitting systems onto us…
I think a lot of adults deserve this treatment in media. I know not all cultures are the same, but I've written extensively of the disdain and hypocrisy displayed by older generations for the youth in America. Just this week my Facebook was filled with adults mocking the opinions of survivors of a school shooting because they are kids and don't know any better. And not just because they disagree.
We live in a time when parents post videos of their emotional (if not physical) torment of their children and they get a million views and fan clubs spring up around how "no nonsense" they are. These same people expect to be respected (read: deferred to) whether they behave respectably or not. The older generation has voted away the ability of teens to work in any but the most niche, boring, and limited capacities, all in the name of "protecting the children" (not protecting their own wages from the competition of younger workers I'm sure) then get on Facebook and bitch about the lazy youth who do nothing all day but play video games.
If we generalized about gays, transexuals, women, the elderly, or any given ethnicity the same way we generalize about "teens," if groups of people laughed uproariously at the targeting of any of these groups for the sort of public humiliation children are breezily subjected to, there would be protests in the street. Those making such videos or telling such tales of any disempowered group other than "youths" would be rightfully excoriated in the media and called out for the prejudiced and hateful behavior that it is, and spend the rest of their careers in sackcloth and ashes as they should.
But children are an okay target. Don't ask me why. But I'm not surprised at all to see this sort of trope in response to such mentalities.