Seeing Double

When I was in wearing my editor hat, there was one writer who drove me crazy. He double-spaced every single sentence he wrote, no matter how many times I pointed out that it was incorrect.
I spent many many hours using find/replace to rid myself of all that extra space.
Any style guide used by a writer, journalist, or editor points out that a single space between sentences is the correct (and only) way to separate them.
So why do so many people not only use that double space, but also insist on it being correct? Slate has come to my rescue with a well-researched answer. The short version is that it's the old-fashioned typewriter's fault. You can read the article here.
We haven't used typewriters (or their old-school type) for years, so I wish that all you high-tech computer users would stop being so spacey.