Beaming in from somewhere else on this not quite Stop Cyberbullying Day anymore day: Reasons to be polite and decent to other people in online fandom, noting that none of them have anything to do with niceness or censorship (or BNFs—Big Name Fans—but the influence they have on the discourse is a little particular to fandom communities).
Some reasons to be polite and decent to other people in online fandom, or in fact, many communities:
5) Among your audience there is probably at least one person whose good opinion you value, or who is in a position to do you either good or harm, who knows and likes the person you are about to be vile to.
8) [The person you are about to flame is] clearly considerably less intelligent than you are, and you have too much pride to shoot fish in a barrel.
9) [The person you are about to flame is] clearly considerably more intelligent than you are, and you have too much sense to invite a slapdown you’ll still remember in painful detail when you are 90.
10) Appearances online can be deceiving. The fact of someone being very new to fandom, or just very young, or alternately much older and not terribly tech-aware, does not actually guarantee that they are not, for example, one of the world’s leading authorities in the field you are discussing. This can lead to, once they have mastered the, for example, [LiveJournal posting] learning curve, and can express themselves clearly, a really really unpleasant burning sensation as your entire body turns flaming red with shame.
13) Something tragic or traumatic will probably happen to you one day, and that will be a bad time to discover that you’ve established a reputation as a person who doesn’t deserve or appreciate sympathy, kindness or tact.
14) One of the many ways in which fandom is not like high school is that fandom is full of extremely smart people. We are not short of clever around here. The bar for "So smart you will automatically be loved and admired, even if you behave like a wild squirrel brought indoors" is set much, much higher than you think it is, and you are probably in no danger of concussing yourself on it.
16) If your motive for nastiness is that you are terribly, terribly annoyed by stupidity, you may want to keep in mind that intelligent and meaningful conversations rarely break out in the middle of vicious slapfights.
Unfortunately my main response to this is that it sounds like fandom in particular, or at least online fandoms that the author of that post is in, pays back your sins much more effectively than geekdom as a whole does.