I've listened to interviews of Kip and Reb Beach recently who said Beavis and Butthead killed their career at the time.
I was thinking about this, ever since you posted it, but I think Kip and Reb are missing the point. Beavis and Butthead were just parroting the zeitgeist, not creating it. Hair metal was done, and then done again, and had devolved into mostly crap and too many ballads by 1991. When something new (Nirvana / grunge) came along, the masses were already primed and ready to jump off that 1980's metal hell train.
I was never a fan of grunge, unless you put early Smashing Pumpkins into that genre, but people were ready for something a little less fluff and a little more heart. I remember reading a Rolling Stone magazine interview ca.1993 (maybe Axel Rose?), where the 1980's metal interviewee put it perfectly. It went something like this: "Music will always go back to the garage. Every time things get too commercial and too over-produced, there will be a reset back to the garage, and that's what grunge is." The reason I associate it (in my mind) with GnR is that Appetite of Destruction, which was absolutely huge, was a bit of a little "back to the garage" reset right in the middle of the 1980's metal and pop scene, itself.
The shame of it is, through all of the hair metal crap, there were some really excellent metal bands. Eg. I always liked Metallica, and they seemed to continue with commercial success right through the grunge era, even after the posers (Poison, Warrent, Motley Crue) all died.