Honestly, this whole thread is full of generalizations.
Most casuals don’t hate hardcore players, most hardcore don’t hate casuals either, thats why you will find threads like this have replies who A) replicate the hate, B) goes against the hate or C) position themselves with hate on the other direction
but being, honest, just like there is this current dislike for hardcore players by some people, there have been a dislike for casuals, some comments here show that and some threads in the past too.
similar reverse topic of a couple years ago https://us.forums.blizzard.com/en/wow/t/casuals-are-ruining-the-game/
Catering to casuals has effectively ruined class design in this game
and back during cataclysm/mop i remember the feeling being quite similar due to quality of life changes blizzard gave like making purple gear more acessible, making pugging easier, raid finder being created and then flexible raiding.