Gosh, Danforth, aren't you sufficiently intelligent to discern the answer yourself?
Here's the paragraph in which the statement is made.
In view of the general declarations of the legislature and the specific findings of the Court, obviously we cannot say as matter of law that the grounds do not exist, and, if they exist, they justify the result. We have seen more than once that the public welfare may call upon the best citizens for their lives. It would be strange if it could not call upon those who already sap the strength of the State for these lesser sacrifices, often not felt to be such by those concerned, in order to prevent our being swamped with incompetence. It is better for all the world if, instead of waiting to execute degenerate offspring for crime or to let them starve for their imbecility, society can prevent those who are manifestly unfit from continuing their kind. The principle that sustains compulsory vaccination is broad enough to cover cutting the Fallopian tubes. Jacobson v. Massachusetts, 197 U. S. 11. Three generations of imbeciles are enough.
Apparently other solutions have been developed.
Instead of "... waiting to execute degenerate offspring for crime ...," the courts today have excused them from culpability and they are not subject to execution because of diminished capacity. So it is their shortcoming that insulates them from the consequences of their behavior.
Instead of "... to let them starve for their imbecility ...," society has provided sustenance for them and thus encouraged their breeding and proliferation.
Of course, this has a political impact as groups that go beyond mere demagoguery, intervene to utilize these misfits for attaining political power, going to institutions for the feeble minded and impaired aged, registering them to vote and casting absentee ballots for them. Those functioning a rung above these unfortunates, are induced to support programs directed to their receiving something for nothing in the form of giveaway programs, welfare overtly and in the euphemistic form of "negative taxation," a euphemism for money paid as welfare through the tax system, Food Stamps, medical care programs, various service programs, and the like.
The current economic debacle originated with a social engineering plan to provide housing to people unable to afford it, eliminating screening for ability to repay loans, and packaging partially secured paper and mandating its marketing through Fannie Mae and Freddie Mac, which were under an order to accept and sell it.
This continuing increase in the indigent constituency with burgeoning welfare programs, threatens the effective functioning of this republic as irresponsible people marshal support for programs that take from the productive and provident and give to the non-productive and improvident, as if no adverse consequences would ensue.
With the existing demographic progression, demagouges are in the ascendancy as the growing portion of the population is dependent because it cannot function in the socio-economic context that comprises a modern society.
In lieu of sterilization and limiting the growth of the segment of the population that lacks the competency to function effectively, the voting franchise should be limited to people who had an obligation to pay taxes during the year preceding the election, and who paid those taxes.