I thought this was a strange fit for the General (non-GB) board, so I moved it. I really could have fit in the Movie or Animation boards just as easily, but picked Video Games because you did mention the games and it isn't as full
I'm not sure where the "Slimer is evi!" thing came from either. I remember some of the previews of the Slimer stage of the video game had people going "All right! Slimer is evil again!"
Some of it probably has to do with reaction to Action Hero Slimer from the post-JMS era, or from a faction of movie snobs who look down their noses at anything that comes from the cartoons.
JMS's preferred use of Slimer is definitely the best: a hungry pet who annoys Venkman, and best used in small doses.