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Spiderman has a very good plot and a reason to be a hero. Iron Mans suit makes since because he had a background as a weapons company and energy company. Hulk makes some since because he was mutated by radiation that exists. Captain America is basically a soldier on steroids, so he is realistic. Need I go on?
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Superman is from another planet and his cells are super charged from our suns radiation. Batman's parents were killed in front of him so he wants to stop criminal activity like that. Marvel and DC have a lot of parallels. What else?