Strange, but I keep routing for Kevin Bacon

Kevin Bacon does have that likable quality, he has a great sense of humor even in his commercials.

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The Id in all of us rooted for Kevin Bacon. (Granted, Bacon's villainous protagonist is the only interesting character in the whole movie.)

Originality needs a reboot.

All the characters are generic Paul Verhoeven character types in a movie that featured a stock slasher movie plot.

Same. I haven't seen this movie in years, but I watched it a few times as a kid and I always rooted for Kevin Bacon's character.

Part of it is that Bacon is a very charismatic guy and is naturally likeable, and part of it is that a big chunk of the story is told through his perspective and thus makes you sympathize with the character.

Kevin Bacon has a strong screen presence that none other cast members have.

He could've gone back to the elevator after he put out the fire and removed his clothes.

I root for Sebastian big time.
The movie is told from Sebastian pov. It's his movie.
The authors want you to smipathize with him, obviously. Even if he's really a "monster".
He's cool, succesful and a genius. And he's played like he's a victim of the circumstances, that bring out the worst in him.

That's blatant because the other characters are not that likeable after all: he is the "hero".
If you think about it, Brolin's character IS a leech and a mediocre scientist using his friend's success; Sue IS a shitty ex girlfriend screwing his buddy and co-worker under his nose; all the other scientists are annoying, mediocre and unlikeable.