Farhad Manjoo gets almost hysterical at the idea that anyone who was writing something would put two spaces after a period. He seems to feel it's worthy of the Death Penalty at the very least.
I'm undecided on whether it's wrong to use two spaces but I have decided that if you do, it's not as heinous a crime as he claims…and I think he's missing one key point. He's correct (apparently) that typographers are pretty unanimous in insisting that there be but one space after a period…but at least in some cases, I believe it's because it gives them more control when they set type. If the size, leading and font selection in a given piece of type seems cramped at the ends of sentences, it's easy for them to add spacing or just tracking there; not as easy to take it away. They're not claiming that type never reads better with a little extra spacing between sentences…just that it's preferable to make it controllable.
Then there's this: Manjoo is correct that the idea of putting two spaces after a period is a leftover from when we worked on typewriters with non-proportional spacing. He says…
Today nearly every font on your PC is proportional. (Courier is the one major exception.) Because we've all switched to modern fonts, adding two spaces after a period no longer enhances readability, typographers say. It diminishes it.
I think it depends on the font but let's get past that. Let's say it's wrong with a proportional font but right with a non-proportional like Courier. Well, guess what: We haven't all switched to modern fonts. A very large percentage of my work is in screenplays and scripts and the custom there is still for Courier.
I put two spaces after a period. There. I admit it. I've been writing professionally for more than four decades and I've always done it that way. This site is written that way, though it doesn't show because the software usually takes out the extra space. It's a habit I could probably break but then when I worked on a screenplay that uses Courier, it would look wrong…and I sure don't want the distraction of trying to remember to space twice after a period in some of my work and once in other projects. I have to do it one way or the other and I say I'd lose more from putting one space in after a period in Courier than I would by putting two in other writing…especially since the two don't always show up.
So I've decided not to try and break the habit and to go on inserting two spaces after a period when I type. If Farhad Manjoo doesn't like it, I don't care. He doesn't read this site.