Justification was used because people thought equal width columns looked better. Columns of text are generally unnessary in the digital world because you can have one infinitely long column.
In Grid Systems in Graphic Design (1981) the author argued against justification because he thought having spaces of different lengths between words created a poor rhythm (I will find the exact quote tomorrow).
But most publications using justification initially didn't use columns, e.g. books.
I do think multi-column layouts are sorely underutilised on the web. Modern websites make a mockery of desktop wide-screen displays where they use about a quarter of the screen and fill the rest with adverts.
In Grid Systems in Graphic Design (1981) the author argued against justification because he thought having spaces of different lengths between words created a poor rhythm (I will find the exact quote tomorrow).