Always in tandem with propaganda I feel. So it would censor criticism of the regime, and any opposite viewpoint, while replacing all voices with the pro-regime voices instead.
I'm not sure this is the same as letting one freely voice their hate of another and propagate lies and falsehoods about them.
I guess you see it as let's just all use propaganda and defamation against each other, and hopefully that evens out where we all meet in the middle through constant bi-directional propaganda and hatred.
But I see it more as let's not allow the use of propaganda and hate anymore, because those things are at the detriment of other people's freedom, and you should only be free to do what doesn't take away freedoms from others as well, unless it has been agreed between both parties through a contract and a system of laws.
I don't really have a proof that one would have better outcomes over the other, but personally I find having a civil debate in good faith with rational arguments is more pleasant than to have a demagogue debate in bad faith using appeal to prejudice, emotions, desires, falsehoods and defamation. So I'd rather we as a society needed to engage respectfully, rationally and in good faith, and I wouldn't mind this to be enforced both culturally and by law.
I've heard the "slippery slope" and the "what if that just radicalizes demagogues even more" arguments, and the latter one I find more possibly valid. I feel the slope isn't that slippery personally, like the slope would only slip if the person in power was again a demagogue ruling in bad faith, and at that point it be too late anyways, since they'd already be in power.
Now the argument that it could radicalize demagogues further, by giving them more ammo to justify themselves, I think that's a more plausible prediction. I'm not too sure about this bit yet, so I could be convinced here, but I'd need to also be convinced that letting demagogues continue to have large public reach isn't itself a bigger threat.