Look at this ad image for the Kindle Paperwhite. Especially look at the third line, and see how the right justification has placed huge spaces between the words, thus making the line horribly difficult to read. This is why you either have to have a ragged right margin, or (if you're going to justify the right margin) you have to hyphenate.
This would *not* make me buy a Paperwhite. It would do the opposite.

This would *not* make me buy a Paperwhite. It would do the opposite.

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