When I took a typography and poster design class in Switzerland this past August, the advice about justification was the opposite: always use justification as a reasonable default that machines can handle and only use ragged right if you have the time to adjust each line by hand. Proper ragged right text should alternate long and short lines in a specific way that algorithms can't handle (deciding if/how to break up words and lines, perhaps even modifying the content to fit). This was coming from Lars Müller and typographers with decades of experience so I'm inclined to trust them, but the alternating ragged lines still looks a bit unnatural at first if you are used to MS Word style text alignment. Once you see it done properly though it's hard to miss when it's done poorly.

Their advice was for physical media while typesetting for the web is clearly a different beast. Trying to emulate print media is a great way to create a poor online experience.