As Ivan the Terrible said: Not Enough!

Compulsory sterilization programs are government policies which attempt to force people to undergo surgical sterilization. In the first half of the twentieth century, many such programs were instituted in many countries around the world, usually as part of eugenics programs intended to prevent the reproduction of members of the population considered to be carriers of undesirable genetic traits.

The first country to concertedly undertake compulsory sterilization programs for the purpose of eugenics was the United States. The principal targets of the American program were the mentally retarded and the mentally ill, but also targeted under many state laws were the deaf, the blind, the epileptic and the physically deformed. Native Americans were sterilized against their will in many states, often without their knowledge, while they were in a hospital for some other reason (e.g. after giving birth). Some sterilizations also took place in prisons and other penal institutions, targeting criminality, but they were in the relative minority. In the end, over 65,000 individuals were sterilized in 33 states under state compulsory sterilization programs in the United States.[1]

Most sterilization laws could be divided into three main categories of motivations: eugenic (concerned with heredity), therapeutic (part of an even-then obscure medical theory that sterilization would lead to vitality), or punitive (as a punishment for criminals), though of course these motivations could be combined in practice and theory (sterilization of criminals could be both punitive and eugenic, for example). Buck v. Bell asserted only that eugenic sterilization was constitutional, whereas Skinner v. Oklahoma ruled specifically against punitive sterilization, for example. Most operations only worked to prevent reproduction (such as severing the vas deferens in males), though some states (Oregon and North Dakota in particular) had laws which called for the use of castration. In general, most sterilizations were performed under eugenic statutes, in state-run psychiatric hospitals and homes for the mentally disabled.[3] There was never a federal sterilization statute, though eugenicist Harry H. Laughlin, whose state-level "Model Eugenical Sterilization Law" was the basis of the statute affirmed in Buck v. Bell, proposed the structure of one in 1922.[4]
-http://en.wikipedia.org/wiki/Compulsory_sterilization

I think it is a good idea to sterilize the rest of the natives. We should grant them the dignity and the mystique of extinction. Am I kidding? Probably.