Dark Continent isn't that bad
After reviewing all the information we have, there are many inconsistencies and knowing Togashi, it can't be a coincidence.
I will elaborate chronologically
First, Don Freecs:
I think this character is being overestimated far too much. He was surely an impressive Nen user, on par with Ging or Netero but not a Nen God. He went to the Dark Continent after forging his reputation in the human world (I think D. Hunter might be the more or less romanticized legend of Don Freecs). On the Dark Continent, where he spent about thirty years (he might have tamed a flying animal like the giant butterfly/moth to facilitate his travels (might be a Feeecs capability to connect with animals as we saw with Gon)). Then he studied the Calamities, so he spent several months or even years with them and he didn't mentionned being harmed. He also discovered fabulous resources that could have advanced humanity. After his time exploring the Dark Continent, he returns to the human world (about 300 years ago), je created or helped create the Hunter Association to facilitate the exploitation of the world and, by extension, the exploration of the Dark Continent. He bequeathed his book, "Est," to the presidents of the Hunter Association to encourage exploration of the Dark Continent. He might have gone back to the Dark Continent, awaiting the next explorers to help them, or perhaps he could have ended his life in the human world as well, leaving the task of writing the West section to the Hunter Association.
Secondly, the aftermath of Don Freecs:
In the 300 years since Don Freecs' return, humans gone to the Dark Continent, they realized the risk of not securing all the resources for their country and then boosted the danger of the Dark Continent. They may even have falsified Don Freecs' book. Why? Simply because they are humans and that could miror what Netero said to Meruem about the infinite malevolence of humans. Of the 149 expeditions, only 5 returned. But what if it wasn't wildlife or Calamities that had eliminated the 144 who haven't returned? What if it was the humans who had killed each other to be the only one who brought back the desired resource and be a hero for centuries? Because Don Freecs manages to safely spend a lot of time within the Calamity's Territory and has probably safely taken their resources, but other humans can't? Even of the five expeditions that returned, none of the few survivors were able to return to their former lives. Because of the calamities, according to the different States. But I think it's for them to avoid revealing that the Dark Continent isn't actually that dangerous. The "museum" of the Dark Continent that the V8 possesses with the victims of the Calamities? These could be real victims who were tasked with testing the capabilities of the Calamities.
Thirdly, Netero's presidency:
So, we all know Netero, he is a manipulator and a liar. And he went to the Dark Continent. Twice. He himself stated (after going there twice) that there was no point in continuing to go to the Dark Continent and banned any further expeditions ... His pal Zigg brought back Ai, a Calamity that has the power to grant any wish in exchange for something in return. Totally no point of having such power, that's true. Furthermore, Beyond waited for (or even orchestrated) his father's death because of the blockade on exploration. Netero's embargo on Dark Continent explorations is merely the result of the previous 300 years.
So that's pretty much it ! Hope you could find some of this interesting and sorry for all the weird English it's not my language 😅