Is there a sociological concept or theory that refers to the phenomenon where members of a society, or groups within a society, hold others down and the whole society goes in a bad direction?
Perhaps 'Lateral Violence', is what you're looking for, although it is not strictly related to sociology. Where members of a group perpetuate violence towards other standout members instead of contending with oppressors/opponents, etc.
I've added an article from Jaber et al. if you think the concept can be helpful to youArticle Indigenous Women’s Experiences of Lateral Violence: A System...
There is a long tradition of writing about elites, especially associated with Mosca and Pareto, and recently revived which examines related questions.
I think that the concepts of "social decay" and "social cohesion" deal with this. Social decay is what happens when there's extreme economic inequality, so social institutions do a poor job of sufficiently providing for people's needs. Under these circumstances, consequences can be catastrophic. Lack of social cohesion is affected by economic inequality, but there are other factors that contribute to social cohesion and the lack thereof.