The trick seems to be to rebel against the conventional in a way that's perpendicular to it, not merely —as most rebellions are— a sign flip?
Yep. If it’s a sign flip it’s not really a rebellion because it’s operating from the same dysfunctional paradigm.
I feel that it is important to point out to native english speakers that the word "decadent" shares a root with decay, and simply means a decayed rotten state, a decline. It is perjorative. There are no implications of 'opulence', unlike the common usage of "decadence" in English as a sort of slang to describe a rich chocolate cake, for example.