The Implication of Social Contract on Social Relations Hobbesian, and Lockean Contractarianism, as a conceptual political framework, entails sacrificing individual "natural" rights, because it presumes that human nature, when left to its own devices, would produce chaos. Therefore, a government would be required to mitigate and control these excesses. Implicit to this view, is that government is distinct from human nature.
This distinction between government and human nature was anathema to Spinoza and, later, Diderot and other thinkers of the Republican Democratic persuasion, who, while agreeing with the Contractarianists that it was in humanity's best interest to join together to form a government (albeit a republican one, contra Hobbes), argued that such a socio-political configuration was an extension of human nature, rather than apart from it.
What is correct in schopenhauer's opening analysis, is that, assuming a Contractarianism framework, it would be perfectly acceptable for individuals or minority groups to sacrifice their rights or their "nature" (think LBGTQ, or religious or ethical minorities) in order to maintain a wider group cohesion. This is how Locke is able to argue for intra-toleration between Christian sects only, rather than wider, full toleration that includes Jews, Atheists, and other religious minorities, as Spinoza argued for.