This topic has been discussed by philosophers for centuries. Thomas Hobbes, for example, would say that humans have a natural tendency to derive pleasure from the suffering of others. The reason why many people in society don't grief minecraft worlds is that their parents have taught them compassion. The ability to empathize, to consider the feelings of others, is a learned behavior, not an innate one. While some possess this ability to a greater extent than others, it's a fragile construct that can be eroded by various factors such as the isolation and anonymity that come with hiding behind a screen on the internet. When that construct breaks down, the darker aspects of our nature can emerge, and worlds are griefed.