Granted that such prevention is a proper function of society, the question again arises whether it is an ethically correct procedure to allow these potentially undesirable parents to marry at all. Should they be doomed to perpetual celibacy, or should they be permitted to mate, on condition that the union be childless. The eugenic interests of society, of course, are equally safeguarded by either alternative. All the other interests of society appear to us to be better safeguarded by marriage than by celibacy. Adding the interests of the individual, which will doubtless be for marriage, it seems to us that there is good reason for holding such a childless marriage ethically correct, in the relatively small number of cases where it might seem desirable. Though such unions may be ethically justifiable, yet they would often be impracticable; the limits will be discussed in the next chapter. It is constantly alleged that the state can not interfere with an individual matter of this sort: "It is an intolerable invasion of personal liberty; it is reducing humanity to the level of the barn-yard; it is impossible to put artificial restraints on the relations between the sexes, founded as they are on such strong and primal feelings." The doctrine of personal liberty, in this extreme form, was enunciated and is maintained by people who are ignorant of biology and evolution;[79] people who are ignorant of the world as it is, and deal only with the world as they think it ought to be. Nature reveals no such extreme "law of personal liberty," and the race that tries to carry such a supposed law to its logical conclusion will soon find, in the supreme test of competition with other races, that the interests of the individual are much less important to nature than the interests of the race. Perpetuation of the race is the first end to be sought. So far as according a wide measure of personal liberty to its members will compass that end, the personal liberty doctrine is a good one; but if it is held as a metaphysical dogma, to deny that the race may take any action necessary in its own interest, at the expense of the individual, this dogma becomes suicidal. As for "reducing humanity to the level of the barn-yard," this is merely a catch-phrase intended to arouse prejudice and to obscure the facts. The reader may judge for himself whether the eugenic program will degrade mankind to the level of the brutes, or whether it will ennoble it, beautify it, and increase its happiness.