Double-spacing is simply the way I had always done it. When someone at a previous workplace pointed out that this style is no longer accepted, I balked and said, "But I've been double-spacing after periods since I was little boy." And that was true.
Sometime in the late 70s my parents gave my older brother a Sears brand manual typewriter. I don't have an actual photo, but it looked just like this:
It wasn't easy to quit. When that coworker pointed it out to me and I verified that the modern preachers of punctuation did indeed frown upon hitting the space bar twice after periods, I begrudgingly conceded and tried to cure my addiction.
This is not something you can quit cold turkey. My first step was to type a document on the computer and then go back through it while proofreading and delete all the extra spaces. Others suggested using the find-and-replace function. After a while I got to the point where I would space twice after a period and then immediately catch myself and hit the backspace key to eliminate my error.
A couple of years later, I could finally type and, without thinking about it, not double-space after periods. (But if you ever catch me double spacing, please let me know.) And now when I read other people's documents, it stands out blatantly if they're still doing it the old fashioned way. Clearly I have crossed over to the other side. I'm cured.