Negative freedoms at least have the virtue of creating the room for you to do what you want to do, whereas 'positive freedoms' seem too often to entail the freedom to do what someone else thinks that you should do. Or as the New Labour officialdom is fond of saying these days, 'its informed choice that counts' - meaning if you choose to do what we think you should, then that is the well informed choice, but if you smoke, or bottlefeed your baby, than that is an uninformed choice.
Harvey seems to be very left wing when he is rehearsing Marx's critique of capitalism, but whenever he has to describe the alternative, it is post-war Butskellite mixed economy state socialism of the kind that made Thatcherism (and punk rock) look like a positive alternative.