Many herbivorous animals have extensively large guts. Herbivores that do not have very large guts often have gizzards (chickens and ostriches) or simply do not efficiently digest all of the vegetable matter that they eat. Think of horses and their kin when you think of marginally efficient digestors; they often have rather whole vegetable manner in their feces. Obviously equids are not the worst animals when it comes to digestion, but they do not have the enormous guts that dinosaurs like Stegosaurus had. Stegosaurus stenops, as the largest species, most likely had the longest gut, though we cannot be certain that it was the widest gut. The small head of Stegosaurus was built for clipping and grinding vegetation for days without ending. The life of Stegosaurus was most likely dedicated to eating, not being eaten, and occasionally mating. The mating part of their life may have even included some raising of young, though the extent of hatchling rearing for Stegosaurus is not known. Juvenile stegosaurs are known from many fossil remains, but the youngest animals are missing from the records, for the most part. A hypothesized family group can be seen in the second Jurassic Park movie (The Lost World) and the idea of the small family group makes more sense than a multiple clutch of young creating a small herd. A sizable herd of any kind of stegosaurs would have been difficult for most predators to deal with as a single adult was difficult for most predators.
The spikes on the end of the tail were significantly dangerous to predators and other herbivorous dinosaurs alike. Officially called the Thagomizer (after the late Thag Simmons), the set of spikes varied by individual and species with S. sulcatus possessing distinctly larger spikes than the other two species. The tail and hypothesized maneuverability of the rear end of Stegosaurus would make for a deadly combination. It has been stated, by Bakker in The Dinosaur Heresies, that the hindlimbs could have been anchored and used as a stable platform while the rear end of Stegosaurus was rotated with significant force if not accuracy. This hypothesized action has been applied to a documentary in which a couple of stegosaurs caught in mud attempt to fight off ceratosaur and allosaur attackers. The point is that the rear end of the dinosaur is shown moving about in the highly mobile and strong manner described. It is much more likely that the tail end of Stegosaurus was mobile and useful as a defensive and offensive weapon than as a passive deterrent incapable of being whipped around as an attacking weapon.