The inverse of this seems to be taking hold now: that it’s socially acceptable to say things which are unreasonable, outlandish or downright factually incorrect, if they’re considered to be in service of a cause that ‘our side’ believes in. But yes, this has also been discussed a lot here before.
Here’s a very old debate: https://en.wikipedia.org/wiki/1860_Oxford_evolution_debate
There’s a good quote inside:
”Let us ever apply ourselves to the task, feeling assured that the more we thus exercise, and by exercising improve our intellectual faculties, the more worthy shall we be, the better shall we be fitted to come nearer to our God.”
The gist I get from it (not saying it’s 100% right) is that we enrich ourselves by exercising our mental state, which means challenging ourselves, exploring new intellectual points, and having the fortitude to go through with it (and hopefully find meaning).
Instead, the easy way is to forgo such “intellectual exercise” and simply regurgitate the same sentiments back to ‘the group’ and drown out the ‘other side’ with self-serving, dribbling retorts.
With respect to “What can’t be said”, this reinforces conditioned thinking that is black or white with no gray area in between to formally discuss. Instead, the ethos is “You’re either with us or against us”, and challenging that classification is violating Rule #1.