The phrase "thought-terminating cliché" has been making the rounds on social media recently. Like a lot of logical fallacy buzzword clusters, this one has a vague, loosely-defined structure, with a semi-sociological origin, and is primarily being used by contentious idiots to bludgeon each other with a big swooshy thwack as the novelty of its phrasing swings heavy across the dumb suckers in your mentions. It's popular in the parts of the web where people like to say that things are "just like 1984" and "Orwellian", out of a vain belief that identifying logical fallacies and calling them names is sufficiently persuasive to prove you right.
The general idea is that certain clichés are used to end thought and discussion; by simply saying them, you are calling for the listener to cease thinking about the topic. For example: "agree to disagree", "who really knows" and "it is what it is". While it seems innocuous at first, the cognition-limiting conditioning of cults and POW brainwashing have been observed using phrases that are in a similar structure: designed to stop the independent thinking of their members/prisoners.
But trying to politely end an argument is not the same as brainwashing a freshly shaven cult initiate, or brandishing a foreign prisoner into accepting your propaganda. The 1953 interviews with Korean War prisoners of war, conducted by Robert Jay Lifton and published in Thought Reform and the Psychology of Totalism, where the phrase "thought-terminating cliché" began its catchy, quickly feared and transmitted life, involved enhanced interrogation techniques and an environment of constant control, power, and threat. Lifton writes that the psychological transformation intended for the prisoners, suspected of being foreign spies, was to "die and be reborn", and that it was achieved with lasting effects. Only in a milieu where there is "overwhelming pressure", constant terror and interrogation with a limited number of options do these phrases gain their "brainwashing" potency.
"centered on all-encompassing jargon, prematurely abstract, highly categorical, relentlessly judging, and... deadly dull..."
This is, of course, different from the setting of discourse between free persons. Without the psychological pressure and the absolute power that a guard has over a prisoner, the use of conversation-ending phrases does not amount to cognitive control or whatever totalitarian voodoo has been attributed to the origin of this idea. A banal equivocating quip does not "suppress cognitive dissonance", despite the catchiness of this particular buzzword and the temptation to use it when you can't come up with a good response. While there is a rhetorical strategy inherent in the attempt to cease discourse when it would not favor your interests, this is not a torturous or psychologically unfair tactic. In fact, it's probably more polite than the typical argumentative snipe.
However, the loosely defined verbal action of using a well-worn phrase which serves the interests of ceasing conversation does exist and can be manipulative. Here, the effort is not to square the disagreements and settle up, but rather to zoom out and away from the subject, put into a bigger frame, and then from the distance of a single defining sentence, render some kind of wide, sweeping statement. Doing this severs the semantic links between the ongoing argument about the internals of the topic and engages with the subject in the past tense. It is essentially saying -- here's a broad observation about the conversation which has just been ended.
"At the end of the day..."
"Despite it all, you have to admit..."
"Say what you will, but..."
It's important to recognize that the cessation of discourse is not a neutral outcome, but instead one which favors the status quo. Conversation has the power to change the arrangement of things, and by neutralizing that potential, the existing hegemonic influences remain dominant. Suppose that we were on the way to go get ice cream, and you said that you wanted to get frozen yogurt instead. If we were to end the conversation with a glib "agree to disagree", that doesn't result in a change of plans, and so we default the original plan of getting ice cream. The employer of this tactic wins, not by actually promoting the merits of their idea, but by neutralizing potential for departure from the current arrangement. In fact, they get two rounds of influence here: once by ending the conversation on their terms, and again in the chance for phrasing the last word in a way that contains their personal opinion.
The criteria for what exactly defines a thought-terminating cliché is not well-articulated. The Wikipedia article contains a circular definition that this phrase describing disingenuous manipulation only applies when there is fallacious logic present: it's only fallacious if it's fallacious. In my opinion, it's fine when, during discourse, there is an entirely natural desire to eventually bring that discourse to a conclusion. Instead, problematic disruption occurs when there is a bad-faith effort to search out dissent, and then inject the comments with a sentiment that induces movement away from the productive ongoing conversation.
"I'm just saying."
"Nothing can be done about it."
"Don't be so surprised."
Honestly, a lot of platitudes, idioms and generally profound-sounding drivel can be used in this manner. No matter what the conversation is about, the tendency to wrap it up in a neat little package with a quickly understood phrase as a summary of its contents will be an effective call to ending the conversation, and on the terms of the person who used the cliché.
On the other hand, if someone is simply trying to escape from a topic that they were bored with 10 minutes ago, then it'd a dweeb move to try and keep them bogged down in it until you finish. It's questionable how useful it would be to call out "thought-terminating cliché" when you see it: if you want to continue the conversation, then the correct move would not be to highlight and attack the word choices of your opposition, but instead to say something useful and to the point. They're trying to wall you off, so say something that still needs to be said. And if there's nothing left to say, then maybe the conversation doesn't need to continue.
"We'll see about that."
"Results, not excuses."
"I see you. I hear you."
There's also the usefulness of terminating thoughts. It's a well established truism in Alcoholics Anonymous that "your best thinking got you here", and the suppression of unhealthy, addictive thoughts is central to their daily effort. Some more cynical people would compare this to cultic suppression of free thought, but removing agency from lower desires is an important aspect of self-control. Deliberately using phrases and mantras which halt reactions to triggers is an empowering mental technique against addiction.
On a final note: when the phrase "thought-terminating cliché" is used on social media, it frequently results in a shifting away from the current topic and onto that particular accusation. Or, it sometimes shuts down conversation entirely. It's a common observation that the declaration of "thought-terminating cliché" can itself be a thought-terminating cliché. This is perhaps a source of infinite ironic recursion, as making such an observation on the phrase has already become a cliché, and it isn't great for the thread of continuity either...