Humans pollute mostly out of ignorance. However, the worst pollution is caused by deliberation. There are a small number of humans who control this issue, and they chose not to correct pollution practices. In some cases they do so for greed, for the cost factor. In some cases they do so out of laziness. In some cases they do so because they don't want to take the heat by calling attention to their past practices. Change would be questioned. But, in some cases these humans pollute deliberately for no other reason than to enjoy the power this brings to their sense of self. This is not unlike the sense of power the sadist gets when giving pain.