There is a battle being waged, and most of the world is wondering why. Every so often I come across somebody who argues, "The modern world agrees, only one space should come after a period." And they feel very strongly about this, arguing with the vehemence of a crusader!
Many assertions are made, usually revolving around typography, typewriters, courier font and the like. The problem here lies in the partial information being presented. Regardless of what style guide X may say, style guide Y generally says otherwise. And style guides change monthly anyway.
There is a very good explanation of all the details behind this at the Heraclitean River blog, so I will not dig too deep into the details, but I urge you to review that information if you feel strongly one way or the other.
Suffice it to say, in summary, as long as layout has existed there has been "additional space" after a period. This is a good thing as it helps us to denote the end of a sentence, especially if you are a speed reader (as I am). Furthermore, the modern software that renders and works layout of a program can also easily address this spacing challenge automatically, so really, it just isn't that big of a deal.
My suggestion is to follow the general style guides I have found that assert, "use one or two spaces, whichever is your preference, but keep it consistent."
My preference is two spaces when I write.
If you use a modern word processor that supports "regular expressions" in a search and replace, you can also easily switch using a regex:
And replace it with a period and one or two spaces as you desire.
Stop making this an issue people. Please.