Having the ability to speak anonymously allows for people to speak their true mind and show their true personality rather than hiding behind the fear of lash back.
I've met some of my best (online) buddies on /b/ or in /b/-related activities (though I don't go there anymore).
Yes, it's a raging shithole of trolls, mouth-frothing idiots and general retardation, but there're probably just as many decent people there. They're just not as vocal. This applies to many places, by the way, not just /b/.
Also, generally speaking, /b/ is the worst kind of example that you can probably think of. This makes for an interesting argument though: it can hardly get worse than /b/ - it's the absolute superlative of anonymity induced uncivility.
