Fiber is great but it's not ESSENTIAL.
It doesn't take much of an effort to incorporate into the diet though, so there's no reason in this day and age for Westerns to abstain from it. Especially when you think of all the crap that's in our foods. I've actually been thinking of doing a colon cleanse for a while now. Also starting to up the fiber a bit. I want to be shitting like a champ soon.