We were probably guilty of that as the Ultras. It was frustrating for existing ST holders but it naturally grew out of that area (top of East Stand), where singers have always congregated and many of us already had season tickets. The more displays, flags, singing and bouncing around that occurred encouraged more to get involved. More fans wanting to get involved meant it kept getting better and bigger but you were then strangled by not being able to congregate in that area due to the space being so limited and congested. It then creates division between those wanting to make something happen and those who have always been there and don't want anything like that happening around them.
It leads to fans buying tickets for somewhere else in the stand and "bundling in" to join the group. It was at that point I knew we needed our own unreserved seating area in an emptier section of the ground to grow it further. However there isn't a single part of the ground where there isn't at least one season ticket holder who's had that season ticket since the stadium opened and will probably feel uncomfortable with it. Although it came close the club didn't want to upset anyone and told us to get on with it, that's where the progress strangled and it ended up petering out.
The only way of making real progress is the club making an unreserved singing section where flags can be waved during the match and the allocation will be reduced. They have to weigh up making significant improvement in atmosphere vs upsetting a few to do so. For me, at least in the past, that was the most important thing about a match day. I was more concerned about the atmosphere being good than about OUFC winning on the day, but I'm probably in the minority there. I think every club has good and bad footballing spells throughout the years but the one constant you remember about each club is the atmosphere you experienced.