More recently, this subject arose on another forum in response to news that Microsoft Word will start treating two spaces after a period as an error and will flag text as such.
As a part of participating in this discussion, I cited that article. I also started looking over other articles on the archived Heraclitean River site and I ran across a followup article that I hadn't noticed back in 2015. This article responds directly to many of the modern-day justifications for single-space sentence separation pointing out that they are either logically incorrect or are inconclusive.
In a previous post, I explored the history of spacing after sentences, where we saw that the common practice for centuries was to include a much wider space after a period (or other mark that ended a sentence). Since a double space nowadays imitates that practice—which comes from the era where the forms of many of our modern fonts were created—a double space should at least be considered an acceptable choice when typing or typesetting text. Others will prefer the single space, but it is merely a preference. I submit that there is room for both, and there is actually room for better typography in general, which could return to a more detailed distinction between different types of spaces with different widths.
I also summarized the history of the Chicago Manual of Style, which demonstrates the shift in preferences and values from 1900–1950, leading up to their current judgmental position where they only include information on sentence spacing to condemn anyone who would try to make such a distinction. In a Q&A post, one editor explains this position and offers a number of rationales in favor of it:
