When we're reading written text, we're just looking at words in order, at the speed we want.
So what the hell does it matter whether it's broken into paragraphs or not?
Whether you read
Comment 1
Comment 2
Comment 3
or Comment 1 Comment 2 Comment 3
Your eyes read the same letters with the same meaning in the same order. Why does it matter whether there was some space between them?
Yet paragraphs have a huge impact. Not only as a reaction, but even if I'm thinking 'paragraphs shouldn't matter, just read the text as if it had them', long paragraphs are still hard to read.
It doesn't really make any sense why. It's not speech, where the speed a person is talking, the pauses they take, are relevant. Want a break reading a paragraph? Wait a moment before going on to the next sentence. Rationally that should be fine, but it's not.
It's not really that different with other 'white space' or punctuation. If there weren't any periods, it wouldn't change the words; you could stop if you want. But having that period makes it more readable. So Comment 1. Comment 2. Is quite different than Comment 1 comment 2.
So it seems that replicating speech patterns in written text - pause here, take a break there - is more important than makes any sense for it to be. Again you could have the same pauses and breaks if you want without the white space.
Try reading an overly long paragraph, and it's hard to get through. It's as if the whole thing gets jumbled and grows in weight so you can't stand to keep reading it, all because there aren't a few blank lines.
It's strange.