"The existence of cheap contraception and murder creates the choice. I doubt that there are many women who haven't used contraception voluntarily."

You do talk crap sonetimes. The biggest fall in the UK fertility rate was in the latter part of the 19th c. In 1830 The average woman had over 5 children. By 1930 it was already below replacement rate at 2.01 This correlates with decreasing child mortality: previously half were destined to die, so fewer replacement babies were required...one of the major factors in the fall of the mortality rate was increased hygene: never underestimate the power of the common availability of cheap soap.

This all happened long before the modern advent of cheap readily available contraception...which itself never stopped the advent of the only period rising above the replacement rate: the post war baby boom.