self Interest

In any situation, there are often multiple goals or outcomes that are desirable. Unfortunately, oftentimes these goals are conflicting. When that happens, it requires some action, a prioritization or a compromise outcome in order to proceed. For example, recently we saw a conflict between the desire to provide universal health care and a desire, held by many, to keep the Government from growing larger.
In an ideal world, some compromise would be worked out that provided the most benefit to both sides. However, it is more common for these competing objectives to be resolved in favor of the stronger party. When this happens, it often creates resentment that builds up over time. It should also be noted that the “stronger” party is often not really the stronger party if social conventions are ignored.
When the rich and powerful impose their will on the poor and weak it usually requires the acquiescence of those very same poor and weak people. When the imposition turns to oppression, we see violent reactions that disrupt society and lead to an overturn of the established order. History teaches us, that given enough time, those conditions will most likely revert to what they were before, but during the unrest some members of the old order are deposed and some of the poor and weak rise to better positions.
Of course, many modern societies, particularly developed Western societies, have worked out a compromise where the middle class serves as a sort of buffer. They generally are well enough off to want to protect the established order and numerous enough to keep the oppressed from taking power.
Of course, we see the deterioration of the middle class, as some of those with the ability to do so, try to manipulate them out of existence.