The notion that truth is found when the pendulum swings to one extreme, and then to the other, and finally settles in the middle is based on the popular understanding of the Hegelian dialectic of thesis, antithesis, and synthesis. Obviously the dialectic doesn't apply to contradictories. If the thesis is "Objective truth does not exist" and the antithesis is "Objective truth exists," then there can be no synthesis. If we are dealing with contraries, then the synthesis is not necessarily true because it's possible for both propositions to be false.
Many Catholics believe that mainstream orthodox Catholicism is the immovable center from which it condemns both "Spirit of Vatican II" progressivism and SSPX-style Traditionalism from an equidistant position. I don't think this is accurate. For one, the SSPX is a specific organization that was until recently excommunicate. It has a specific leadership with which to negotiate and hopefully reconcile. Liberalism on the other hand is more like a cancer which has infected entire national hierarchies. The Church can approach the SSPX as a problem external to it. The most outrageous liberal offenders are often members of the hierarchy in good canonical standing. In many corners of the world the progressives ARE the Church. The SSPX is made up of four bishops, about 500 priests, and maybe half a million lay Catholics who assist at their chapels. The Archdiocese of Los Angeles alone is home to 4.3 million Catholics. It strains credulity to argue that radical Traditionalism is in any way a comparable threat to the demonic Spirit of Vatican II.
We must make a distinction between an error and an incomplete truth. Error plus error equals more error. Determinism, for example, is an outright error that all right thinking people reject. "Man has free will" is true, but it's an incomplete truth if we fail to distinguish between freedom and license. An incomplete truth can give birth to errors if we claim that it is complete when it isn't. The opposite of an incomplete truth is necessarily error. For example, it's true that we must love our neighbor for the love of God. One extreme would be to see our neighbor as only the means to the end of serving God without taking any interest in our neighbor as a person. "I think you're a useless scumbag but I'll help you out cuz God says so." This is an incomplete truth but it's not an outright error. The opposite extreme, which is an outright error, would be to say, "I'm going to help my neighbor because I'm a nice guy. God doesn't have anything to do with it at all."
Our culture has been generally moving leftward for decades. Left-liberals are in the vanguard of the ongoing revolution while right-liberals bring up the rear with impotent grumbling about the speed of the changes while rarely questioning the changes themselves. We are all of us caught up in the Hegelian Mambo. The Hegelian Mambo (learned from Zippy Catholic who learned it from somebody or another) goes like this:
In practice, this means a conservative is whatever a liberal was 30-50 years ago. Altar girls, communion in the hand, and receiving the Precious Blood at Mass were once absolutely forbidden. The Vatican strenuously protested these practices, but the various national bishops conferences ignored them. Finally, after a decade or two, the bishops essentially said "These are traditions of the people now and you can't make us stop doing it." The Vatican caved. Now many Catholics defend these practices by saying, "The Vatican and the popes said they're okay so that makes them good and laudable, and you are an odious Trad dissident if you say otherwise."1. Move further in a leftward direction.2. Make the few unprincipled exceptions you are going to make, even while still moving in a more leftward direction on other issues.3. Display your unprincipled exceptions for all to see, fooling conservatives to accept you as a conservative yourself, especially those conservative whose positions are a matter of tradition, piety and religious faith, but who themselves do not have a strong intellectual defense against leftism.4. Eventually your positions are accepted as the new “conservatism” by most people.5. Hold to these positions for a time, either because you are not yet bothered by some of your illiberal positions or because you need to shore up support.6. Start the dance all over again.
As the left moves ever leftward, the right, defining itself as opposition to the left, moves leftward itself. Divorce was once unthinkable but the left argued, "Divorce must be a more readily available option or else women will be trapped in loveless marriages and the children will suffer!" Then it became "Divorce shouldn't require having to prove fault. This is a private matter!" And so on down the line until right-liberals are slowly lining up to support same-sex "marriage" because they don't want to be on the wrong side of history and all that. Fifteen years from now conservatives will be arguing that humans and beasts should have the option of civil unions but not marriage. Fifteen years after that they'll be arguing that humans can only marry one animal, not several.