What an ironic sight.

Outside Prestatyn Magistrates' Court in Wales, nine online bullies – who had named and vilified a teenage rape victim – struggled to conceal their identities behind umbrellas and documents after being ordered to pay compensation for their vile actions.

In contrast to their apparent shyness, each had used Twitter and Facebook to spout venom towards the 19-year-old following the rape conviction in April of footballer Ched Evans. The former Wales and Sheffield United player had been sentenced to five years in prison.

Having endured not only the rape, but also the subsequent police investigation and trial, the victim was left further traumatised by the heated online exchange that revealed her identity. She was accused of being a "money-grabbing slut" and a "dirty slapper". "She's to blame for her downfall," wrote one Facebook user. "Let's find her address."

The group, which included a cousin of the footballer and a biology teacher, were each ordered to pay £624. While this paltry sum is an insult, hopefully the guilty verdict will help hammer home the message that the online community is not above the law, despite the informality associated with social networking and the cloak of invisibility provided by user names.

One of my few memories of studying philosophy was Plato's argument, in Republic, that a man's true worth could only be revealed by his actions while he wore a ring of invisibility. He asked whether anyone granted the freedom to operate outwith the scrutiny of his peers would behave badly. As an idealistic student I was appalled at the suggestion that a person would only be compelled to act justly to please an audience and would otherwise wield his power unfairly and selfishly. However, the existence of trolls would seem to support this.

Early exponents of the internet dreamed of a place where people could freely exchange information and ideas. However, the freedom to hide behind user names, coupled with the de-humanising vastness of the virtual world, provides a depressing answer to Plato's question.

Much as I applaud the idealistic notion of internet freedom, that must come second to preserving the dignity and privacy of individuals. Trolling and online abuse ruins lives. Only last week, a young teenager in Ireland was reported to have taken her own life following an alleged bullying campaign.

Ched Evans's teenage victim has had her life ruined once by the shameless actions of a footballer. It has now been ruined over again by bullies who robbed her of the chance to try to put the crime behind her and start afresh. Rape convictions are already pitifully low. If the thought of being identified and abused online by friends of the attacker crosses a victim's mind, we risk dragging this already depressing statistic down to zero.

The nine argued they hadn't realised that what they had done in naming the victim was a crime. But didn't it occur to them that what they were doing was morally wrong? Clearly not, but the "didn't-know-the-law" argument is pathetic. If you want to play the online chatter game, read the rules. Just as journalists must abide by defamation laws when publishing, whether in print or online or broadcasting, so must users of social media.

Commenting on the case, a lawyer said it sent a "public health warning" to those who treat social media as "a conversation", and a number of recent cases should serve the same purpose among those who claim ignorance of the law. In March, 21-year-old student Liam Stacey posted racially offensive comments about Bolton midfielder Fabrice Muamba as the player lay in intensive care following a heart attack. Last September, Sean Duffy was given an 18-week sentence for posting abusive messages online about schoolgirl Natasha MacBryde after she committed suicide.

This latest case took abuse a step further by not only demeaning and defaming the victim, but stripping her of the right to anonymity that is enshrined in law and therefore her chance to try to pick up the pieces of her life and move on in private. While the verdict is a step in the right direction, by choosing to impose only a relatively light fine the judge has pulled his punch at the vital moment.