Harold David was delighted. The 34-year-old New Yorker had not been sure what to expect when he downloaded NGL: maybe some of the anonymous messages he got via the app would be very rude. But, he says, "it was actually a warm flood of responses about people's experiences with me, so it was a really nice surprise".

David is one of more than 15 million people around the world to have used NGL. The app invites anonymous questions and comments from followers on Instagram, Twitter and other media platforms.

"It's fun to see what people will say when it's anonymous," David explains. "Who wouldn't want to know someone's secret thoughts on them?"

Not everyone shares his view. Reggie Baril, a Los Angeles musician, expected to get interest and encouragement from people about his career. But in the 130 responses he received, he found "more hate than not".

One of them called him "a social climber". Another said: "You could be so successful but your attitude is awful, you won't make it."

Other users have had questions and comments which seem to come from bots rather than real people - but because they are anonymous, it is hard to be sure.

Online anonymity is a deeply divisive issue. Those who oppose it point out that it allows people to say hurtful and deceitful things that they could not get away with if everyone knew who they were.

According to Valeriya Safranova, writing in the New York Times, anonymous messaging apps usually end up being withdrawn because of "unfettered bullying, harassment or misinformation".

Two, Yolo and LMK, are being sued by the mother of a teenager who committed suicide after being bullied online. Messages on Yik Yak caused several schools to evacuate pupils after threats of shooting and bombing.

Premier League players have received thousands of abusive messages. One survey found that 56% of these were racist.

Incidents like this have brought calls for laws to make social-media users sign in with verifiable identification. This would discourage abuse and make them easily traceable if they broke the law.

But for others anonymity is both highly attractive and vitally important. According to Professor Sherry Turkle, an expert on people's relationships with technology, it allows you to "speak something true that you can't in the rest of your life". Being able to confess feelings that you have always kept quiet about can be a huge relief.

Anonymity can also be a matter of personal protection. Without it, according to Amnesty InternationalAn international non-governmental organisation focused on human rights. , many people would be at risk - among them "human rights activists who challenge the authorities, journalists who uncover corruption and lawyers holding powerful governments to account".

Other vulnerable groups include persecuted minorities, victims of domestic abuse who are hiding from their attackers and whistle-blowers.

In repressive countries like Russia and China, the government has banned VPNs to stop users from hiding their identities.

Yes: As things stand, anyone can post appalling abuse on the internet, or pretend to be someone they are not for grooming or other criminal purposes. Compulsory ID would put an end to that.  

No: It would spell the end of freedom of speech online. Many people would no longer dare say what they feel or express political opinions, for fear of being persecuted or thrown into prison.   

Or... All social media platforms should give users a choice about receiving messages from people they do not know. Sensible people know that using an app like NGL is asking for trouble.