This statement illustrates a consciousness that would be dangerous for an Outer Party member to have, so it is possible that O'Brien shares the same consciousness as Winston, but because of his status in the Party, has no reason to want society to change. He is not the individual being tortured, though he would have Winston and the reader believe that the "rehabilitation" once happened to him as well.
O'Brien is often seen as a father figure and a friend to Winston. O'Brien is trying, through torture, to make Winston "perfect," to "save" him. If Winston would simply embrace the Party's doctrine, he would be "clean." But it is not really Winston that O'Brien and the Party want to change; the Party wants to purify all thought, believing that one stray thought has the potential to corrupt the Party.
The character of O'Brien is not so different from many of the contemporary leaders of the 20th century. For example, Hitler and Stalin used this kind of torture to keep their power and did it in the name of "purity." O'Brien represents these leaders and others, who use cruelty and torture as their primary method of control.
