I'm a couple of years younger than Julian Assange and commonly use two spaces after each sentence, purely out of muscle memory. (I took a "keyboarding" class in 1987 or so using an IBM Selectric typewriter and that's the way I was taught to do it.)
I'm not at all surprised that many people still do this. I'm a little surprised that people assert that's a "proper" way to do it or for that matter get worked up enough about it to write that you should "never, ever" do it. Maybe it's the engineer in me, but I was expecting an actual negative consequence of using two spaces. Typography is important, but I'd guess that with modern kerning techniques the difference between two spaces and one is slight. (In fact, if I were designing a word processing app, I'd think this is is a case I'd account for: If there is a "proper" distance between the period at the end of one sentence and the start of the next letter, wouldn't you ensure that's the distance that is used whether the user typed one space or two?)
Yes, LaTeX ignores anything more than one whitespace in the source. It does, however, automatically insert extra space after a period. (Unless you disable it with the ~ symbol, e.g. after the word Mr. or e.g.)
I'm not at all surprised that many people still do this. I'm a little surprised that people assert that's a "proper" way to do it or for that matter get worked up enough about it to write that you should "never, ever" do it. Maybe it's the engineer in me, but I was expecting an actual negative consequence of using two spaces. Typography is important, but I'd guess that with modern kerning techniques the difference between two spaces and one is slight. (In fact, if I were designing a word processing app, I'd think this is is a case I'd account for: If there is a "proper" distance between the period at the end of one sentence and the start of the next letter, wouldn't you ensure that's the distance that is used whether the user typed one space or two?)