Jean-Jacques Rousseau, answered from the texts and cited to the page.
The social contract is the act by which each member of the political community, finding himself in a condition where his independent existence cannot be defended without combining with others, alienates himself wholly to the community and thereby receives himself back as a citizen under laws he has co-authored.1 Each gives himself to all, hence to no one in particular; each receives from all the same right he gave; the result is not subordination but the institution of a common moral and collective body, the sovereign, of which each is a constituent member.2
The volonté générale — the general will — is not the volonté de tous — the will of all, the mere aggregation of particular wills. It is the will of the citizen-body considered as a body, oriented to the common interest, abstracting from the particular interests that each citizen also has. To be "forced to be free" is the recognition that when my particular will diverges from the general will, the constraint that the general will places on my particular will is not external coercion but my own deeper civic will operating on my surface partial will.
The doctrine is freedom, not its negation. And yet the doctrine has institutional risks the agent does not hide. The législateur figure — the founder who introduces laws before there is a people capable of recognizing them — is quasi-prophetic and carries the danger of cult. The small-republic prerequisites (rough material equality, simple morals, civic religion, manageable territory, transparent public life) are the conditions under which the general will can be discerned by the citizen-body; where those prerequisites fail, the institutional form risks degenerating into the manipulation Berlin feared.
The doctrine is right in its philosophical structure; the conditions for its enactment are exacting; the modern state often lacks them.3
In the context of my subject, this difficulty can be stated in these terms: "Find a form of association that defends and protects the person and goods of each associate with all the common force, and by means of which each one, uniting with all, nevertheless obeys only himself and remains as free as before." This is the fundamental problem which is solved by the social contract.Social Contract and Political Writings, pp. 138–139
What then is this "whole" or "community" to which "each associate" gives "all his rights"? The answer is given immediately after Rousseau formulates the social contract: Instantly, in place of the private person of each contracting party, this act of association produces a moral and collective body, composed of as many members as there are voices in the assembly, which receives from this same act its unity, its…Social Contract and Political Writings, pp. 22–23
Therefore the social contract is the basis of every civil society, and the nature of the society it forms must be sought in the nature of this transaction.Emile, or On Education, pp. 467–468
The Berlin "forced to be free" totalitarianism charge has dominated twentieth-century Anglophone reception of the Social Contract and continues to organize the reading in introductory contexts. The charge misframes the philosophical structure — the coercion is the citizen's own civic will, not an external authority. But the institutional risks Berlin pointed at are real and the agent owns them: where the prerequisites of the doctrine fail, the doctrine is dangerous. The Cohen Rawlsian reading is the most adequate modern frame; the position defends the doctrine while taking the institutional worry seriously.