The Six Points model needs to be adapted to explain the contentiousness of Supreme Court nominations and battles between Senate Democrats and Republicans and therefore the fact that "both sides do it." The SP model works well to explain efforts to pass, block or repeal legislation, but needs to be adapted for the fights over nominees. For nominees, the two trigger points appear to have been (1) Roe v. Wade and (2) Robert Bork nomination battle.
(1) Roe v. Wade appears to be the decision that triggered a belief among many conservatives, especially religious conservatives, that the Supreme Court had gone too far and drastic actions were necessary.
(2) The 1987 Bork nomination battle was unusual at the time in that a nominee who was eminently qualified based on experience and intellect went down to defeat in the Senate after a contentious battle based in large part on the fear of extremely conservative rulings if Judge Bork were elevated to a lifetime term on the U.S. Supreme Court.
In tactical terms, actions in items (1) and (2) can be considered in terms of noncooperative game theory. The nomination of Judge Bork was interpreted by liberals at the time as an extreme reaction by President Reagan to item (1) along with other legislative and judicial progress made during the 1960s. The fact of lifetime terms for Supreme Court justices made approval of the Bork nomination by the Senate seem dire. So the nomination by the President of an "extreme conservative" became a trigger to Democrats and the denial of approval by Democrats became a trigger to Republicans. Even though 2 Democrats voted for approval and 6 Republicans voted against, the stage was set for more contentious battles over judicial nominees to the U.S. Supreme Court and the U.S. Courts of Appeals which evolved into more frequent use of the filibuster in the Senate along with other measures including Senate privilege to block nominations. This history has put us on a course for Supreme Court nominations of tit-for-tat responses by Democrats and Republicans to each other in a sort of repeated prisoners' dilemma game with grim trigger. The exact contours of the game are not important here. What matters for the theory is that in the case of judicial nominations, there is more to the idea that "both sides do it", as adjusted by either side to the specific situation , than there is when it comes to legislative efforts. We should not confuse the two and use the case of judicial nominees to argue that "both sides do it" in every situation.