I would be interested to understand how you came to the conclusion that he argued for both sides? I saw a scathing repudiation of the socialist utopians of the era (and 'rational' ideologues of all sorts). He 'argued' their sides too, but with the goal of making them appear ridiculous. By the time Raskolnikov's fictional essay about the "extraordinary" comes up, i think it's pretty clear what Dostoyevsky is trying to say. Though that's just my interpretation.