Perhaps someone can publish a paper to arXiv that provides a meta-analysis. But still there doesn't seem to be a clear reason to justify it, given that almost all internet text is not justified.
Having a two-column theme, or left-aligned vs justified themes, could be workable in the long run. I hope that we get to see some browser extensions modding the pages before too long.
The reason for the current justified text is that it is the default aesthetic for a LaTeX-based article, and a lot of authors expect it.