The United States, as the name indicates, was formed as a confederation of independent states-initially only 13, but since expanded to 50. The first Federal government was based on The Articles of Confederation, but that was abandoned because it gave too little power to the Federal government. It was replaced in 1787 by the Constitution. Many governance rules have been a compromise between the growing power of the federal government, and the original vision of the country as a confederation of states that retain much of the legislative powers.
Posner describes the evolution of the Senate from a few members appointed by state legislatures to a much larger body elected directly by the voters of each state, where each member serves a 6-year term that is renewable indefinitely. Small states, like Rhode Island, have the same number of senators as the most populous states of California and New York. The Senate is an anachronistic byproduct of the original concept of a federation of states since in the modern world the federal government dominates state governments. The potential influence of a relatively small number of states is increased by the supermajority rule that is embodied in the filibuster.
The Senate filibuster is not a part of the Constitution, but is a rule the Senate established. However, the protection the filibuster gives to minorities does fit in with the belief of the founders of the nation that the power of majorities needs to be constrained in order to protect the interests of minorities. The Constitution, and the checks and balances among the executive, legislative, and judicial branches of government, are important ways they devised to rein in the power of majorities.
Whether someone likes or dislikes the use of the filibuster on particular issues usually comes down to whether they like the legislation that the majority is trying to pass. However, the evaluation of the Senate filibuster as a legislative rule should depend on whether filibusters have blocked desirable legislation more than they prevented the abuse of power by a majority, especially power by a temporary majority. Its main use during the past 70 years is not reassuring since Southern senators filibustered on several occasions against civil rights legislation in order to protect discrimination by Southern states against blacks. However, their filibusters did no more than delay the passage of this legislation, and the delay gave time for the South to become reconciled to the necessity of giving Southern blacks more equal rights.
The mere threat of a filibuster has sometimes discouraged the bringing up of bills in Congress, although these threats also probably only temporarily delayed passage of legislation with a strong and sustained majority interest. Even senators that oppose particular legislation hesitate to filibuster legislation that has a strong mandate since they risk becoming unpopular. Yet they may use the threat of a filibuster to extract a compromise more favorable to their position.
The use of the filibuster has been rising over time: the 110th Congress had over 100 closure votes to try to cut off further debate. The Democratic majority in the present Congress seemed intent on achieving a "filibuster proof" majority of 60 members. Yet, as Posner discusses, having just the minimum number of senators that can enforce the closure rule gives considerable bargaining power to Democratic senators who do not strongly endorse the Democratic position on particular legislation.
I generally support requiring super majorities in the legislature on a selected number of major issues because I believe the abuse of majority power is a greater danger in the world of big government than is the blocking of the majority's will. To be sure, the Senate filibuster is not the ideal way to do this, partly because it is not confined to major issues, and partly because the Senate is based on representation by states rather than by population. Nevertheless, the filibuster may well be better than the alternative of having just straight majority voting in both houses.