El Rol de la Izquierda

En un MUY interesante comentario Johan Norberg se pregunta algo que me temo tiene mucho de verdad: si el rol de la izquierda es sólo la oposición por la oposición misma a las ideas liberales o de derecha, sin nada que aportar:

So many leftists just oppose anything liberals and the right propose? Have they never heard about principles, convictions and drawing conclusions from reality, rather than from columnists? It seems like a form of politics driven less by a desire to improve the world, and more by an interest in fighting and restraining groups you dislike for other reasons. They hate liberalism more than they love socialism.

And this is also a second hander´s view of politics - the person who does not rely on his own judgment, but on the judgment of others. But the big mystery is why leftists would rely on the judgment of the right when they outline their policies. Would they oppose flowers and ice cream if the right was in favour?