I don't understand. BSU fans are passionate, and of course I'm a fan of both since I grew up in the Boise area. I've been to BYU and Boise State games and didn't see very much vitriol, and least nothing compared to BYU/Utah games or the old BSU/Idaho rivalries.
In my experience BSU fans don't really dislike BYU, for the most part. For most of the time, BYU didn't win enough to be considered a rival, anyways. Which is probably why some BYU fans have had a problem with BSU fans and most BSU fans hardly ever even think about BYU.