Please explain the logic of the following sentence (in boldface) in Rousseau's "Discourse on Inequality".
Why would "the children to become burdensome to their parents" cause "murders them all without distinction"?
If I strip this being, thus constituted, of all the supernatural gifts which he may have received, and of all the artificial faculties, which we could not have acquired but by slow degrees; if I consider him, in a word, such as he must have issued from the hands of nature; I see an animal less strong than some, and less active than others, but, upon the whole, the most advantageously organized of any; I see him satisfying the calls of hunger under the first oak, and those of thirst at the first rivulet; I see him laying himself down to sleep at the foot of the same tree that afforded him his meal; and behold, this done, all his wants are completely supplied.
The earth left to its own natural fertility and covered with immense woods, that no hatchet ever disfigured, offers at every step food and shelter to every species of animals. Men, dispersed among them observe and imitate their industry, and thus rise to the instinct of beasts; with this advantage, that, whereas every species of beasts is confined to one peculiar instinct, man, who perhaps has not any that particularly belongs to him, appropriates to himself those of all other animals, and lives equally upon most of the different aliments, which they only divide among themselves; a circumstance which qualifies him to find his subsistence, with more ease than any of them.
Men, accustomed from their infancy to the inclemency of the weather, and to the rigour of the different seasons; inured to fatigue, and obliged to defend, naked and without arms, their life and their prey against the other wild inhabitants of the forest, or at least to avoid their fury by flight, acquire a robust and almost unalterable habit of body; the children, bringing with them into the world the excellent constitution of their parents, and strengthening it by the same exercises that first produced it, attain by this means all the vigour that the human frame is capable of. Nature treats them exactly in the same manner that Sparta treated the children of her citizens; those who come well formed into the world she renders strong and robust, and destroys all the rest; differing in this respect from our societies, in which the state, by permitting children to become burdensome to their parents, murders them all without distinction, even in the wombs of their mothers.