What points can I make if I have to debate about the War on Terror from a socialist/left-wing perspective?
As a socialist, the main thing that you will want to do is to look for economic causes for things. Socialists believe that much of what happens in the world is a result of the upper classes oppressing the lower classes. You could make two arguments in this connection. First, you could say that most terrorism is done by poorer people who have been oppressed by the rich. You could say that, if the rich (in, for example, the Muslim countries) would only be fairer to the poor, there would be fewer poor people who would be willing to become terrorists. Second, you could argue that the US, as a rich country, oppresses the poorer countries of the world. For this reason the people of those countries come to hate the US and want to commit terrorist attacks against it. In both cases, you are trying to make the argument that upper class oppression of the lower classes is to blame for terrorism.