Rivers mean your justification algorithm is broken. It is true that the browser being broken isn't something you can change, but using CSS hyphens and falling back to something like hyphenator.js allows you to have justified text that is basically free of rivers in practice. It's perhaps not as easy as it should be, but it is possible.
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Disagree. Justification causes the so called "River" http://en.wikipedia.org/wiki/River_(typography) that can cause readability problem.
With the relative lack of typographical control on the web right now, it's best to keep text non-justified.
Rivers mean your justification algorithm is broken. It is true that the browser being broken isn't something you can change, but using CSS hyphens and falling back to something like hyphenator.js allows you to have justified text that is basically free of rivers in practice. It's perhaps not as easy as it should be, but it is possible.
This problem is solvable (actually solved by TeX 30 years ago).
Try to read the page on a narrow screen like mobile phone, you will know how bad it is without hyphenation.