my vote is that this thing is genetic, and is triggered by something either in the environment or possibly in the diet as a food intolerance.
I never thought stress played a big role in my uc. I have had uc 21 years, with a 15 year remission from 1991-2006 (in 2001 and 2004 i had other issues emerge though, GERD, +H pylori, gastristis) . And oh believe me i had HUGE HUGE amts of stress in those 15 years. And when you hear about babies and little children getting this, well, they dont have stress.
i do think stress can weaken the immune system, but really who doesnt have stress these days?