(I'm scattered today, so this might not get to the point.)
In the real world, when there's a demand for something, someone usually steps in to supply that demand. Not always; in a superhero world, you have to distinguish between something that you can supply and something you can't. A number of villains want world domination, but that turns out to be difficult to supply. (Most people who can get it won't give it up, although there's an interesting meta one-shot, where it turns out the whole thing is virtual reality, so that Visigoth Feral can finally take over the world...and the sequel is what happens after he discovers the ruse.)
However, in a superhero world, there are a number of things that aren't legal to sell that are still wanted. Vampires and blood, for instance. Blood is not really legally available for sale, but making it available could reduce the total amount of vampire-on-human violence. ("I managed to pay my way through college by pimping humans to be vampire blood bags!") Various radioactive materials are necessary for the life of various supervillains, who would presumably not be indulging in crime if they could just get what they need. 
So supply and demand says that most of the time, if there's a demand, there's going to be a supply. That trade is going to be illegal if the law doesn't recognize it. Sometimes the law is vague or fuzzy; the status of blood as a commodity is one: it falls under some health laws and it might be illegal, but it might not. Most people refuse to sell it because of that gray area. (There's also the question that can't legally enter a contract to buy something because they're not recognized as persons.) Sometimes the law is just slow...it hasn't recognized vampires, AIs, robots, zombies, uplifted animals, and extraterrestrials are legally persons, and can't legally enter into a contract to buy something. 
In your superhero world, there are almost certainly people working in favour of making some of these things legal (Atlantis should be recognized!) and some people against it (What happens to shipping if we recognize Atlantis? Is there a competitive trade advantage to ports that recognize Atlantis, or are the sea-dwellers too scattered or rare to make a difference? Is the threat of terrorism by Atlanteans an acceptable risk? )
The attempts don't have to succeed, but you can have them in the background to give verisimilitude to your superhero world. The idealistic college student who is all about how vampires are only violent because they can't get blood (and who may or may not have suspicious scabs along the femoral artery); the working man who is sure that the current set of anti-invasion laws are sure to make things better for him ("All the interdimensional guys gotta get sent back because they're taking jobs from guys like me!"); the businessman who claims that the attacks by created villains improve the economy (because they stimulate building and repair work, and a certain amount of R&D).
You could even have a presidential hopeful who offers solutions on these problems—the kinds of solutions that make trouble for the heroes.
1. And the water of the fountain of immortality is probably a fair advertising issue: Touting it is outlawed as an unprovable claim, because it takes decades before you discover that you're not going to die.
2. There's always been the question in my mind of why Bruce Wayne doesn't pay thugs to quit crime. In fact, that's part of the appeal of the Wayne Foundation: it's a tool where Bruce Wayne tries to make the world better so that Batman isn't needed. (Which brings in mind the millionaire sketch from Second City: Bruce is out of money, because he's spent it all on thugs and crimefighting equipment. What does he do now?)
3. In my recent Emerald Knights campaign, I had the Atlanteans as freshwater aliens living in the Great Lakes. They were recognized and had treaties with Canada and the USA. The fact that they regarded an area of the lake as taboo played into the game a bit. The early parts of the game are on Obsidian Portal, if you want to look at it. I think it was called something like Steel City or Steel City Blues.