I mean yeah, but best just vote with your wallet and just not engage and the story will die. If more people enjoy the new version to allow it continue and colour future iterations then... maybe its just not for you and the franchise is for a new generation who are voting and do like it. Like I dislike teen titans Go,.. But I honestly seeing how many actually enjoy it, Im just going "I'll never get the OG series back but I guess it probably not for me since so many do like the new version enough to keep it afloat"
It would be nice if people make thier own series but sadly I know getting a new series off the ground is more riskier to a studio than using a premade franchise for intial captial funding. So I can see why this happens.
On that one, its less to do with dark fiction and more to do with using ACTUAL children for its message. Cus if it was simply written or animated or like didn't use LITERAL children, then honestly I'll say let the story stand on its own. But it didn't so yeah, nasty. 0/10.
Rick and Morty Ive mostly assume they more meant dark humor. Honestly seeing the episodes I feel, they just think its funny but dont know the same joke over and over agian isnt funny and more tireing' (something alot of comedy people tends to keep forgetting).... Family guy does it already so, it aint anything new.
As for glorification yeah, albeit mostly cus Ive seen people complain when a series that is meant to unnerve the audience, which I personally find silly. (like complaining a haunted house is scary)... Like come on, its on the box. "Too gorey" my brother in christ the genre on the book is splatterpunk! what else you expected? Sunflowers?
I mean people do have their fetishes and there's nothing wrong, but I rather get into a series with that already warned and prepared rather than it dropped into it no context or reasons and expect me to enjoy.
But non of that has much to do with fan head cannons and more just how media is made 
I mean a fan can eventual, with thier own head cannon go onto a project and change it, but that's less fanon and more what happens when a franchise goes on long enough. Fans become the writers, for better or for worse. Once again as a writer you make your series just have a stronge back bone and steer in your direction. But once again you cannot control how others enjoy a piece of media, just let them enjoy how they enjoy something and enjoy it in your own way. As long as no one bothers anyone (big ask for the internet I know but a guy can dream) it will be okay.