I have not taken a typography class, but norm seems to be context dependent. On the internet, unjustified seems to be the norm, looking at the random high-traffic websites I visited. Printed media is another beast though. I picked up a random book, justified, random newspaper, justified, random marketing material from my mailbox, justified.

So in this current case, since OP's blog is on the internet and not printed, I would suggest unjustified.