Fully-justified text is also generally harder to read for everyone, but for dyslexic folks especially. On the web, this is exacerbated by browsers' relatively poor support for fine, print-quality type layout.
Studies have found that justified text reduces reading speed by up to 11% as the eye has to do more work to find the next word as they’re irregularly spaced.
I did a quick search and found a PDF [0] (page 8) referencing a study from 1986, but a lot of work has been done on typography and readability over the years. Actually, even though it’s pretty old, that document is full of solid design advice.
