nonymity can encourage inauthentic behavior because, with no way of tracing anything back to you1, you can get away with pretending you are someone you are not, or behaving in ways that would get your true self in trouble.
People only act like themselves when they are the ones to face the repercussions of their actions. Anonymity gives people the liberty from facing consequences therefore they tend to act more irrationally. Existentialism says that people are defined by their actions, but if no one ever knew who did them, then actions don't help define anyone.