Trolling is destructive, senseless, yet it offers a glimpse of ourselves. Trolls on /b/, and other online communities, ultimately take advantage of our own societal weaknesses to offend and insult. To condemn the trolls is to condemn ourselves, because if we cannot see the satirical nature of the trolls, we are accepting that their exaggerated racism and offensiveness is grounded in real substance.
Of course, it is certainly not the case that trolling is always racist, or sexist, or offensive in any way. I can hardly see how links to shock-horror pictures or screamers are offensive to anything but my eyes and ears.