Once the portion of single people in a population reaches a critical mass, you have a serious problem with families being at a competitive disadvantage in economic terms when it comes to meeting even their most basic needs. This is why, for example (without even knowing this from any source -- I just know that it is true by definition), the average cost of housing in an area is almost always inversely proportional to the percentage of households comprised of families. This is a particularly serious problem in areas where unmarried couples (heterosexual or homosexual), or married couples with no children, outnumber families.