I do think one of the reasons that people are so angry about the shit show that is Velma.
Is that the OG Scooby Doo show came out in 1969, it’s been with us for 50 plus years.
It’s not just a beloved animated show, it’s a beloved animated show from people’s childhoods for the last five decades.
There are people who grew up with Scooby, sharing the show with their kids and grandkids. A family tradition of sorts, where each generation meets and loves the fandom. Each bringing something new to it, from the books, comics, tv shows, movies, etc.
Something that is so ingrained in the hearts of so many people, especially from childhood is going to be a treasured memory and a part of who that person is.
So when the shit hits the fan this badly, people can get pretty protective of the beloved part that has meant so much to them and has been a part of their lives since childhood.