The rest of society can have different rules which can be more nuanced.
Creating "free speech zones" seems like a surefire way to start telling everyone to "take it to the free speech zone" and stop annoying "normal people" with your ideas. It's like the wet dream of these people that have started calling citizens consumers, even in a political context, and advocate the criminal prosecution of peaceful protesters when they don't all stay on the sidewalks.
FWIW, I first remember hearing the term in the context of the Beijing Olympics, which should tell you everything you need to know about that idea.
I went to university in the United States. The university I attended instituted "free speech zones" in the wake of the (second) Iraq War. They were initially protest zones, but by the time I was there they had turned into what you basically said - places where students were told to go to express unpopular ideas instead of being allowed to express them in class.
I took a sociology course during my studies, and the topic of abortion came up. Instead of having a nuanced discussion about the topic, students objecting to the professor's view were cut off or ridiculed. One student, trying to articulate their position was yelled at, by the professor, to shut up and if they felt strongly enough to take their position "to the free speech zone with the other Christian fascists and religious weirdos". Every year I was there, the bounds of the free speech zone got smaller and smaller, so there was even less room where unpopular ideas were officially tolerated on campus.
This is part of why I got out of academia. Not because of any institutional bias, but the authoritarian bent of the administration. All of campus should be a free speech zone. (No, disrupting class is not "free speech", there is a difference.)
Example from 2004: https://www.acslaw.org/acsblog/free-speech-zones-balancing-f...
Edited to add: But, okay, I suppose "kill all the Jews with Zyklon B"[1] was a novel form.