Huh. I always thought non-justified text existed because people are lazy; I absolutely consider fully justified text to be easier to read, not harder. Non-justified text is distracting.
I'm sure it varies from person to person. I believe, though, the bulk of the studies have found that, while people generally find justified text to look nicer, reading speed and comprehension tend to suffer for it.
Same for contrast. If you're not actually trying to read, low-contrast is more appealing. Thus, the CEO who has read their marketing blurb a thousand times likes low-contrast, even though it's counter-productive.