what is the problem when winston and julia discuss actively rebelling against the party?

Winston is much more concerned with the rebellion from an intellectual, ethical and idealistic point of view. Julia is just happy to stick it to the party through her double life. Julia's aims are not as lofty as Winston's. Julia cares little if a "brotherhood" exists or not. She is kind of like a rebellious teenager sneaking out of her bedroom at night without her parents knowing. At this point Julia does not share Winston's need for enacting revolution or change. She doesn't share Winston's deep philosophical musings nor does she really much care.It is also of note that Julia feels it is possible to prolong this affair whereas Winston knows they are ultimately doomed.