This issue of sectarianism is an interesting one, especially in the context of this thread.
It seems ironic that other sects are declaring that Gelugpas are sectarian. Mainly through the false accusation that Dorje Shugden's practice is sectarian and forbids people from practicing or taking teachings from other lineages - this of course is absolutely not true and there is much documented evidence of Dorje Shugden lamas and oracles assisting Nyingmas, Sakyas, Kagyus.
The ironic lies in the fact that things are segregated - nay sectarian - within the Gelugpa sect itself. Where else do we see as prominent a divide as between Shugdenpas (Gelug) and non-Shugdenpas (also Gelug).
The jealousy aspect is definitely in the mix - this is clear. A Gelugpa cannot speak badly against any practitioner, edict, practice or teaching within any other sect for this is called sectarianism. But this is where the greatest irony is. In NOT being sectarian, the gelugs have turned inwards and creating the greatest segregation and sectarianism among themselves. this is all thinly disguised of course. They flaunt big phrases, like they are preserving the purity of the lineage, protecting the spiritual welfare of practitioners etc. When in reality, all it is, is a blatant discrimination against one particular practice within the lineage. And come on, if that isn't being "sectarian", I don't know what is.