Lindsay Beyerstein in In These Times:
No sooner had Brutsch [a.k.a. Violentacrez, Reddit's top troll] been outed than fanboys started bleating about how it was unfair to expose him because what he was doing was perfectly legal. Which it largely was. The law, as they say, is a blunt instrument. It's easy to forget because it's so pervasive, but most antisocial behavior is held in check by social, rather than legal sanctions. Jerks don't get asked back. Liars and promise-breakers are shunned. The tactless get dirty looks. The indiscreet get elbowed.
In practice, our legal freedom to speak our minds is constrained by our accountability to the people around us. They know who we are, they know where we live, they will kick us under the table when we get out of line. In real life, we only have one body connected to one name, and we've got to weigh the satisfaction of speaking our minds against the long term effects on our reputations and relationships.
This is a pretty elegant system, albeit an imperfect one. It puts the “society” in “free society.” In real life, we have the legal right to say pretty much whatever we want, but we are enmeshed in a network of social checks and balances that keep us accountable for our speech. Nobody can force us to shut up, but lots of people can make their displeasure known to us. It's a good balance that allows people to share ideas freely without rending the fabric of the community.
Pseudonymity is great because it allows people to speak without the usual constraints, but it can also be terrible for the same reason. As ViolentAcrez, Michael Brutsch opted out of all social controls on his speech and ran amok. He could say things he would never have said under his real name because they're rightly regarded as horrifying. Until recently, he didn't have to live as that Hitler/Misogyny/Creepshot Guy (all subreddits he started). He didn't have to endure his neighbors crossing the street to avoid him.