Death to the double space. Viva la revolucíon!
The reason I only use one space between sentences is because the two-space standard is an artifact from manual typewriters. Typists made a practice of using two spaces because otherwise the keys would jam because many typists were too fast for the keys. In the days of the secretary pool, many people, women mostly, had typing as their job, so they got pretty damn good at it. And those old typewriters couldn't keep up.
Once the electric typewriter was invented, the two spaces between sentences standard should have become a thing of the past. My guess, however, is that it remained the standard because the men in charge, who didn't type and only read, thought it looked "weird" after having been raised on the two space standard. As they never typed themselves, they didn't ever experience the annoyance of the double space tap or of needing to go back to double check to make sure that your sentences are properly spaced.
Take a look today at the fields where double spaced sentences are still required. They're either bureaucracies where people follow arcane rituals for no good reason, like government agencies, or professions where the people in charge are old and/or never had to type for themselves, like the law. Because these professions have so much relative clout, they're able to hold out against the vast tide of workers accustomed to using computers and inserting single spaces.
Death to the double space. Viva la revolucíon!