Farhad Manjoo proclaims the vileness of excessive spacing between sentences at Slate:
I was taught to always put double spaces after periods, but switched to single spacing at some indeterminate point after college. I'm not entirely sure whether I ever recieved an angry lecture on the subject (I've certainly run in circles where such things could happen), or whether I just absorbed it by osmosis in working on manuscripts with people who read style guides for fun.What galls me about two-spacers isn't just their numbers. It's their certainty that they're right. Over Thanksgiving dinner last year, I asked people what they considered to be the "correct" number of spaces between sentences. The diners included doctors, computer programmers, and other highly accomplished professionals. Everyone—everyone!—said it was proper to use two spaces. Some people admitted to slipping sometimes and using a single space—but when writing something formal, they were always careful to use two. Others explained they mostly used a single space but felt guilty for violating the two-space "rule." Still others said they used two spaces all the time, and they were thrilled to be so proper. When I pointed out that they were doing it wrong—that, in fact, the correct way to end a sentence is with a period followed by a single, proud, beautiful space—the table balked. "Who says two spaces is wrong?" they wanted to know.
Typographers, that's who. The people who study and design the typewritten word decided long ago that we should use one space, not two, between sentences. That convention was not arrived at casually. James Felici, author of the The Complete Manual of Typography, points out that the early history of type is one of inconsistent spacing. Hundreds of years ago some typesetters would end sentences with a double space, others would use a single space, and a few renegades would use three or four spaces. Inconsistency reigned in all facets of written communication; there were few conventions regarding spelling, punctuation, character design, and ways to add emphasis to type. But as typesetting became more widespread, its practitioners began to adopt best practices. Felici writes that typesetters in Europe began to settle on a single space around the early 20th century. America followed soon after.
Every modern typographer agrees on the one-space rule. It's one of the canonical rules of the profession, in the same way that waiters know that the salad fork goes to the left of the dinner fork and fashion designers know to put men's shirt buttons on the right and women's on the left. Every major style guide—including the Modern Language Association Style Manual and the Chicago Manual of Style—prescribes a single space after a period. (The Publications Manual of the American Psychological Association, used widely in the social sciences, allows for two spaces in draft manuscripts but recommends one space in published work.) Most ordinary people would know the one-space rule, too, if it weren't for a quirk of history. In the middle of the last century, a now-outmoded technology—the manual typewriter—invaded the American workplace. To accommodate that machine's shortcomings, everyone began to type wrong. And even though we no longer use typewriters, we all still type like we do. (Also see the persistence of the dreaded Caps Lock key.)
It's a relatively minor aesthetic point... especially when you consider our browsers make a lot of decisions for us in that regard... but in writing in a word processor I agree with a preference for a single white space between sentences, as otherwise it tends to screw up justified text and leave it riddled with gaping holes. Which is how we come to real aesthetic problem involving Manjoo's column: ragged right text alignment is the typographic alignment of unlettered barbarians and philistines! Oh, but it's so popular you say. Bah! Popular with idiots maybe, but I don't see how anyone can stand it... there's so much evil whitespace at the the end of his sentences that his paragraphs look like KKK rallies. Whitespace subtly and joyously interspersed throughout ones lines to create hard right margins is how the FSM wants us to typeset... shown by His choice of the word "justified" for His preferred typesetting alignment.
EDIT: It's fairly awesome what the Justification gods did right there.