Part of the problem that some of you are having wrapping your brains around how this article could be true stems from a misunderstanding of "functionally illiterate."
We tend to interpret the word illiterate as its dictionary definition, meaning a person can not read at all. There exists a very large portion of the population who can recognize printed words, but can not comprehend what they're reading. Since they are able to look at writing and pronounce the words, we don't associate them with illiteracy. That is where the term functionally illiterate comes in.
These people can look at a sign that says "Kentucky Fried Chicken" and read it to you. They could page through
Green Eggs and Ham and tell you what all the words are. What they can not do is parse a sentence. What they are doing is looking at writing and sounding out a few words. That isn't the same as reading. The ability to read requires more than just looking at words and pronouncing them. You have to understand what you are reading. You have to understand how the order in which those words appear changes their meaning. A good way to spot someone who's functionally illiterate is by whether they have to read aloud. (It's not perfect, but it's a start).
To get a feeling for what the article is saying, consider a piece of writing from prior to the industrial revolution:
Quote:
The quantity of matter is the measure of the same, arising from its density and bulk conjunctly.
Thus air of a double density, in a double space, is quadruple in quantity; in a triple space, sextuple in quantity. The same thing is to be understood of snow, and fine dusts or powders, that are condensed by compression or liquefaction; and of all bodies that are by any causes whatever differently condensed. I have no regard in this place to a medium, if any such there is, that freely pervades the interstices between the parts of bodies. It is this quantity that I mean hereafter everywhere under the name of body or mass. And the same is known by the weight of each body; for it is proportional to the weight, as I have found by experiments on pendulums, very accurately made, which shall be shown hereafter.
Modern readers find that phrasing and sentence structure to be strange. It is not incomprehensible, but neither is its meaning readily apparent the first time your eyes roll over the words. People don't talk that way today. Inability to parse Newton's definition of mass doesn't make a person illiterate. It's meant to show how a person can be able to recognize words and not understand what they mean. Imagine everything you tried to read was like that. The words don't make sense together.
Now, as to how adults who've been at least through the sixth grade can get like that...
Does anyone remember grade school? Does anybody remember the whole class, or parts of the class, taking turns reading aloud from the book? Maybe you did it in third grade, or maybe it continued all the way to seventh if you were going to school in an area that had literacy problems. Do you remember certain kids stumbling over words they were reading?
Children are fascinating. There are quite a number of them who encounter something hard, and then want to give up and have an adult do it for them. I have a niece who's like that. Reading is hard when you're first learning it. She's doing well, but when she runs into trouble she gets very frustrated and wants to sit there and stare at the book until someone tells her what the word is. Luckily for my niece, her daddy reads a lot, and he does it very fast. He's going to make her read herself. What if he couldn't read, though? If that were the case, my niece would only get practice reading in school. A parent who can't read isn't likely to force their child to read. That's very rare.
The problem perpetuates itself. Not being able to do something that you're trying to learn makes you feel dumb, especially when it's very basic. I run into this a lot. Most of my students "aren't any good at math." They are "not math people." They "don't get math." We aren't studying calculus together. They're taking 9th or 11th grade algebra. They want to quit. They want to be as far away from what makes them feel dumb as they possibly can, and I have to figure out a way to stop them from giving up. I don't have this problem with my physics and calculus students. They are willing to accept that advanced math makes them feel dumb, and don't try to retreat into their shells. It's the elementary and college algebra students that want to quit. I don't doubt that English teachers and reading teachers encounter the same hurdle. Teaching people basic fundamentals of reading requires overcoming their tendency to give up when their frustration makes them feel dumb.