The Sith made their choices for power, and are paying for it.
Wait a minute here.. How can the Sith be paying for something if anyone can be a Sith? Is a dark side wielding Wookie paying for the actions of a pureblooded Sith five thousand years ago because they are both equally Sith? Your statement is only coherent if there is such a thing as a Sith by blood who inherits a connection to Sith in the past through which consequences for past actions can flow.
The only common factor now is the Force. It is beyond Jedi and Sith, it unites all living things.
So because all living things have a single commonality they belong in the same group despite being separated by dozens of other differences (such as fur or tentacles or living under water?) This is what I am talking about; the outer boundaries for group membership that you propose are so vague as to be without meaning. By this standard one could say that everyone who breathes oxygen is a Wookie because the only common factor is now oxygen breathing and it unites all oxygen breathers.
My claim was that since they are so ingrained into the Dark Side of the Force now, they've effectively become integrated into a larger spectrum of species that now call themselves 'Sith' for better or worse.
This claim is incoherent because it posits a definitional boundary so vague as to be meaningless. The outer boundary to 'Wookie' is not 'someone who lives in the jungle of Kashyyyk.' Likewise the definitional boundary of 'Sith' is not 'someone who uses the darkside of the force.'
The Force does not discriminate.
The force does discriminate and it discriminates along the lines of species. Some humans are force sensitive. All Dathomirians are force sensitive. The Sith species even had a genetic predisposition toward the dark side of the force. The Rakatans were force sensitive until a plague affected them as a species and they lost their force sensitivity.
@astratitanicus: You made the claim that membership in a culture is contingent upon interacting with some environmental feature. The force, in the case of the Sith. But if you were to extend that logic to the Wookies it would obviously lead to a ludicrous conclusion.
If SW history had been different and the Sith had never encountered another species or left their planet but one day the force stopped existing by magic would the Sith no longer be Sith? That makes no sense. A people's existence as a group with coherent and meaningful boundaries is not contingent upon the presence or absence of an environmental factor.
@astratitanicus: That definition is so broad as to be meaningless. One might say that Wookie culture is rooted in survival in the dangerous forests of Kashyyyk and that anyone who survives in said forest is a Wookie.
Right? The SW lore is much deeper than it may appear on the surface.