The interesting question for us who agree with you is why do other people think otherwise. Two reasons come to mind: some co-workers don't mind the disruptions themselves (e.g. if they do a different kind of work), and some managers simply just like the view.
I'm a cynic and tend to believe that in most cases it comes down to a belief (rooted in short-sighted thinking) that open-plan saves money by compressing more people into a given number of square feet of office space. That is, I think few - if any - managers actually believe that open-plan is better for productivity or anything... they just think it's cheaper, and they don't bother balancing the cost savings with the other factors.