In so many ways, the internet has been a force for good. It enables us to keep in touch with friends and family all across the world. Our children can access the sum total of human knowledge at the touch of a button, wherever they are.
And social media means anyone can have a public platform to express their views, keep in touch with whatever sort of news they are interested in and develop relationships that would never have been possible before. Many parents worry, however, about how much time their children spend online. This generation of children has been dubbed 'the phigitals', because they are the first to draw no real distinction between the physical and the digital worlds.
On average, children are spending nearly five hours a day in front of a screen – not much less than adults who typically clock up six hours gazing at smartphones, tablets and work computers.
That means we need to pay more attention than ever to what we're all being exposed to online. It’s time to confront head on the fact that much of social media has become a sewer. I'm on Twitter and Instagram, and I'm grateful for the fact that they allow me to communicate directly with people who are interested, promote my charitable causes and let people read my own words rather than someone else's slant on them.
But the truth is, a lot about these sites terrifies me. I rarely if ever go 'below the line' on social media or news websites and read people’s comments. I know that a lot say nice things, but there's a large minority who seem to think that all the normal rules of society don't apply to the internet.
Take a look at any website, and you’ll see extraordinarily abusive comments aimed not only at people in the public eye but also other internet users. Bullying, sniping, bitching, even the most appalling sexism, racism and homophobia are commonplace – it seems that online, anything goes.
Women, in particular, are constantly pitted against and compared with each other in a way that reminds me of how people tried to portray Diana and me all the time as rivals, which is something neither of us ever really felt.
People feel licensed to say things online that they would never dream of saying to someone's face, and that encourages others to pile in. It's so ubiquitous that we've all become numb to what's going on. There is good evidence that this online culture is having a detrimental impact on people's mental health, particularly vulnerable young people.
I believe that it's time to take a stand. This isn't about freedom of speech. The truth is, it's not acceptable to post abuse or threats on social media or news sites, and it's not acceptable to harangue other users simply because they disagree with you. It's not acceptable to pit women against one another all the time. It's not acceptable to troll other people viciously online.
Social media companies and news websites need to do much more to take a stand against online abuse, rather than shrugging their shoulders and saying there's nothing they can do about it. And we all, as individuals, need to take a step back and try to make sure that what we say online is responsible and fair.
I'm impressed by the approach recommended by Dr Anthony Wallersteiner, headmaster at Stowe School, where my son-in-law Jack was educated, who is also chair of my charity Street Child. He suggests that youngsters should be taught how to create a positive digital footprint by using the principles of 'THINK before you post' (T- is it true; H – is it hurtful; I – is it illegal; N – is it necessary; K – is it kind?). It's a formula that adults, too, should bear in mind.
So I am pleased to endorse the excellent new #HelloToKindness campaign. Let's all try to think before we post. Let's all try to treat each other a little more gently. Before starting an argument online, take a deep breath and try to respect someone else's position. Where we see others behaving unacceptably, let's call it out. It's an old motto, but a good one: if you can't say anything nice, don't say anything at all.