People who are against diamonds seem extremely aggressive about making sure other people agree with them and validate their opinions. I can't imagine making a website about any of my jewellery preferences (short of ethical, which isn't mentioned prominently here).
Well it's like vegans. Except here instead of animal suffering, it's human suffering; which can give a greater sense of importance to the cause. And in turn, it would make people against diamonds feels justified to be more aggressive.
Their principle problems are price and marketing.