The considerations that lead up to, and, to some extent, justify this desire, will be discussed later.
The fact remains that an increasingly large number of people have come to the conclusion that the burden and responsibility of family obligations limit their enjoyments in life, their ambition, and even their scope for usefulness, and have discovered, through the spread of physiological information, means by which marriage may be entered upon without necessarily incurring these responsibilities and limitations.
It is the knowledge of these physiological laws and the practice of rules arising out of that knowledge, that account for the declining birth-rate of civilized nations.
If it be true that the birth-rate is controlled by a voluntary effort on the part of married people to limit their families, and that that effort implies self restraint and self denial, it would not be too much to claim that those most capable of exercising self-control and with the strongest motives for such exercise, are those most responsible for the declining birth-rate, and that those with least self-control and the fewest motives for exercising the control they have, are most likely to have the normal number of children.
It has already been suggested, that the desire to limit families is due to a consciousness of responsibility on the part of prospective parents.

They realise the stress of competition in the struggle for existence, they are anxious for their own pecuniary and social stability, and even more anxious that the children, for whose birth they are responsible, should be provided with the necessities and comforts of life which health and development require.

They are eager, too, that their children should be equipped with a good education, and thus be given a fair advantage in the race of life.
To the great mass of people this is possible only when the numbers of the family are limited.

As the numbers of the family increase, the difficulties of clothing and feeding and educating increase, and each member is the poorer for every birth, and in this sense an increasing birth-rate is a cause of poverty.

The sense in which poverty causes a high birth-rate will be dealt with later on.
It will be readily conceded, that those actuated by the motives just considered, those with the keenest sense of responsibility in life, those capable of exercising the self-restraint which family limitation requires, constitute the best type of citizens in any community.