I've written many times about the foolishness and destructiveness of open plan offices. Here is a pithy summary of the truth about such plans. If you want to know why they are so beloved of management, take a look at the last two facts.
If you want to know how harmful they are, look at all the other facts. As usual, the oft stated rationale of “increased communication” isn't supported by the facts. Sadly, there is probably little you can do to stop such plans once the bean counters see how much cheaper they are but perhaps the 100% loss in productivity will give them pause. Perhaps.