Perhaps it's because I've been reading voraciously for almost 40 years now, but I can't remember the last time I felt 'threatened' by a block of text. Content, yes, but just the look of it? No.
Conversely, because I am so used to reading fairly quickly (though I admit I do still hear the words in my head), I found the two-space version of your paragraph irritating compared to the more familiar one-space version. I mean irritating like a mental itch,
not irritating like a pet peeve. The visual interruption was rather like listening to someone with a silent stutter--waiting for the next thought made me more and more impatient.
One thing I think people misunderstand when they advocate for two spaces is that a paragraph is a series of connected thoughts, not just a collection of discreet statements. When the flow of those connected thoughts is interrupted visually, it is also interrupted
mentally and therefore harder to follow. This is true for me, and I believe it would be true for most people who are comfortable with written language.
For context, I am a technical editor with a background in writing and editing newsletter articles and marketing material. And as you can see, I am also a firm believer in single spaces after a period. Besides improving readability, it saves time and keystrokes!