[zomozzyk] Depletion of a social class

Some social class decreasing in population within a stratified society seems a somewhat common occurrence, perhaps with enough instances to draw general conclusions about how society responds.  How does society respond?

Examples of depletion of an upper class:

1. Eastern European brain drain during the Cold War, especially prior to the construction of the Berlin Wall
2. Katyn massacre
3. Civil rights reform in America allowing the black middle class to leave segregated black neighborhoods.  The black middle class were an upper class relative to the black lower class, the latter who then suffered in urban decay due to the departure of the black middle class from their neighborhoods.

Examples of depletion of a lower class:

1. Some barrier to upward social mobility becoming removed or decreased.  (Examples?  Maybe public education.)
2. High-casualty war fought by soldiers conscripted from a lower class.
3. Availability of abortion decreasing the incidence of women (and families) becoming demoted in class due to the financial burden of raising a child (that they don't want).  Most abortions are for economic reasons.  Children raised by a parent or parents who don't want them or are unable to support them are less likely to do well in society, so would have gone on to populate a lower class.

This last one was the inspiration for this post.  Fear, uncertainty, and doubt about the large-scale social effects of abortion could explain poltical support of making or keeping it illegal or hard to obtain.  Does depletion of a lower social class cause to the classes above increased pressures and incidences of class demotion?  It seems like it would have to.  This would yield a predictive model of who supports or opposes abortion: those who are most insulated from class demotion will support it.

Previously: (1), (2)