Unkind and judgemental people exist everywhere in society, and as others have said, the anonymity of internet fora makes them bolder in what they say and how they say it, @Kaylasmum49. I am sure this is not a problem that is unique to Mumsnet.
I do usually see people challenging the unkind or judgemental posts, and when you look at a thread overall, you can usually see when the nasty posters are in the minority, and most people are disagreeing with them.
I do also think that, sometimes people don’t like it when they don’t get universal,agreement, or when posters tell them they are being unreasonable (I’m not saying that’s you, @Kaylasmum49 - but it does happen) - and we are told we are all nasty meanies.
On balance, though, I think MN is a great site, full of wise, witty, intelligent, caring people - you only have to look at the various support sections - bereavement, special,needs, breastfeeding, education etc etc, or things like the Woolly Hugs projects, where a legion of MNers knit or crochet squares for blankets that go to bereaved MNers, or the families of MNers who have passed away, or that go to children in hospital, women undergoing cancer treatment (in memory of the lovely Zombie), or refugees, or children in Africa, as well as special white blankets to wrap premature babies who pass away - so the parents don’t see their baby wrapped in a piece of towel or sheet. We also hold online craft fairs, raising money for various charities. And all this grew out of wanting to offer some comfort to a MNer whose 2-year-old died. We were all over the country, so couldn’t bring food or flowers, so decided to make her a blanket, to offer a physical demonstration of our care. Like sending someone a woolly hug - hence the name.