"Just for the sake of argument" seems to mean "so that we can have something to argue about".
Of course, the comparing and contrasting of different opinions is an essential part of the Hegelian dialectic method of reasoning. Every action causes a reaction,and in the world of ideas, the two ideas reach a stasis and a third idea is born.
IDEA: We should be ruled by a king. REACTION: No, the people should rule themselves. ARGUMENT: That is impractical, there must be a leader. SYNTHESIS: let the people choose a leader from among themselves. That is an example of the Hegelian dialectic.
So this sort of conversation can actually be useful.