Before the Utes had beat BYU consistently there was a great deal of animosity built up regarding BYU. In the 80s it was just expected to be pounded by BYU. BYU fans were pretty arrogant when it came to the rivalry. So for some Ute fans acting like complete imbiceles was the the high life during that time.

Second, I grew up in a Ute neighborhood during the time. There were some soci-economic reasons and church activity reasons for the hatred. BYU by the late 80s had become the destination school unlike the Utes in the 60s. BYU also represented everything inactive Mormons hated about the church. I know, I used to be one and have many friends who hated BYU. Weirdly I never joined them due to the persecution in junior high I endured as a BYU fan. But I do understand why the hate is real.

So do those things happen at RES, yes they do despite your denials to the contrary. But lately it's been more gentile except for the anti Mormon element. Those individuals can be particularly caustic when drunk.

Do BYU fans do stupid things, say stupid things, absolutely. But you can't compare the number of these acts to Ute fans due to the factors I mentioned.