Americans that want exceptions to freedom of speech must have no idea what countries that have them use them for.
Framing it as violating a noble ideal of “free speech” I think gives it more importance than it deserves.
Seems plausible such a trade off is a net good for South Korea. We live in the misinformation age. Look at the crazy stuff some people believe. South Korea has effectively outlawed pro North Korea propaganda. Hard to quantify the averted harm of such a policy, but the price seems minimal.
Propaganda can be harmful even if hasn't programmed anyone to welcome an invader with open arms.
Nobody was put in jail for writing poetry. They were put in jail for praising North Korea.
Banning the praise of North Korea isn't banning bad advice.
If the person had been speaking into a microphone instead you'd be telling me how South Korea outlawed talking.