You'd think they would have learned after the second Demon King, but nooo, they have to work hard to recreate the same scenarios that caused the first two demon kings while thinking it absolutely won't go wrong.
@Sep10trion
I don't think the goddess can do much of anything with the current clusterfuck.
Since the world can only survive a certain level of magic, the goddess can't descend to personally take care of it, the summoning was actually a reasonable measure since the first demon king was a threat if left unchecked, the combined magic of DK+Hero theoretically prevents any further intervention because adding a 3rd/4th great magical power would outright destroy the planet, and you can't really trust the humans on that planet to not screw things up even if it was possible to make a new hero. The most magic power she can exert without ending the planet by this point seems to be showing up in the mirror to talk.
TLDR The goddess is getting a bunch of blame in the comments here when humans on their own managed to screw things up so hard that the goddess can't actually do anything.
@icarushector That King is probably the same one that caused the creation of the OG demon lord in the first place and we've all heard stories of how rude/inconsiderate/stupid the overprivileged can be. He is an idiot, but a believable idiot once you think things through. Unfortunately that's the most dangerous kind of idiot since as people we generally tend to assume another person can be reasoned with on some level.
TLDR while it's obvious in hindsight that he (or the rest of the royals would do something, the actions were too stupid to reasonably expect anyone to actually do them.