Amongst the Eight Values of Free Expression, the Discovery of Truth, or marketplace of ideas, in my opinion, is possibly the most important value to understand due to the fact that everything else stems from this ideal.  Through John Milton's writing of Areopagitica, we learn that the idea of marketplace of ideas' main purpose is to bring about the truth, and especially make sure transparency of our governing body is extremely prominent.

The fact that our criticism can meddle with pre-exisitng components to the truth, ultimately creates a high castle for the one and only truth.  Our words can not be manipulated by any party, which fundamentally will create a basis of understanding and knowledge that the truth will always come out.

This free market principle is what extends to the world a designation of free will in countries, as well as shows the world which countries will hide the truth, no matter how cruel consequences could be.

Years after Milton's publishing, a man named John Stuart Mill published a writing On Liberty.  This conceptualized publication brought more insight into understanding the true purpose of a "marketplace of ideas". Attached is a link to a scholarly article published from Middle Tennessee State University.

Link: MTSU-Makretplace of Ideas