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@TheGhostKing151 Ok, think of countries as separate ecosystems, yeah? Well, obviously the citizens and what not make it up, with the big wigs being the big guys calling the shots. Now in our society they are always going at each other's necks and the necks of other big guys in other ecosystems (wars and such). Villains fix that by giving every country in a way a common enemy to focus on instead of trying to one up each other in arms races. Villains are like the predators to keep the ecosystem in check, but too much and it will collapse, so heroes are the predators to the villains, keeping them in check so it doesn't collapse.
Now, what happens when heroes take out all the villains? Well, I imagine since humanity doesn't have a common enemy, it will turn back to wars fighting over land or beliefs, but this time with bullshit super powers.
So the villains and heroes keep things in balance to keep it short, villains to keep the separate environments distracted from wanting to take from each other, and heroes to make sure their own environment from collapsing.
Or another way to put it in like if you removed the predators from an area, the herbivores are going to reproduce more than the environment can carry, which will then force them to move to another one to survive, or everything in the original one dies, so either a new predator is introduced, or humans cull the heads here and there. But if there are no animals, herbivore (villains), carnivores(heroes), then the plant life or small critters (basically everybody else) will grow out of control.
I hope that explains it well, I've been taking a ecology class and I was entertaining a small story idea and this popped up in my head for a conversation between three characters.