Every liberal says this dopey phrase all the time, like its a Tourettes tic.
It's one of those phrases they use to confirm to each other that they are knowing and superior. Normal people can use this phrase to confirm that they have encountered an NPC, ignore it, and keep moving towards their goal.
I think there is an echo here of the old Marxist rant against "traitors to their class".
If you worked for a living (and who doesn't?) then you belonged to the Proletariat and you had an obligation to support the great Socialist revolution. If you opposed the Revolution, you were a traitor to your class -- which is to say, you were acting against your own interests.