The parental sacrifice necessary in rearing the normal number of children is infinitesimal compared with the parental advantage.
Parental love is a passion as well as an instinct in normal men and women, and the full play of this passion in its natural state is productive of the greatest happiness.
Vice may restrain, replace, or smother it, but nothing else can damage or adulterate this powerful passion in the human heart.
Low level selfishness, love of low level luxury, diseased imaginings, and unreasonable dreads and fears, are some of the forms of vice that smother this noble passion.
The pursuit of happiness and the higher forms of selfishness would naturally point to parentage.
The ectasy of parental love, the sweet response from little ones that rises as the fragrance of lovely flowers, self-realization in the comfort and joy of family life, the parental pride in the contemplation of effulgent youth, the sympathetic partnership in success, the repose of old age surrounded by filial manhood and womanhood, all go to make a surplus of pleasure over pain, that no other way of life can possibly supply.
What is the alternative?
To miss all this and live a barren life and a loveless old age. Perhaps to bear a child, that, for the need of the educative, elevating companionship of family mates is consumed by self, inheriting that vicious selfishness, which he by his birth defeated, and finding all the forces of nature focussed on his defect, like a pack of hounds that turn and rend an injured mate.
Or a family of one, after years of parental care and love, education and expense, dies or turns a rake, and the canker of remorse takes his place in the broken hearts.
Nature's laws are not broken with impunity—as a great Physician has said, "She never forgives and never forgets."