Though the words legend and myth do share some common ground, they are not truly synonyms. Please see the previous links for each word -- entries taken from The American Heritage Dictionary of the English Language (Fourth Edition) -- for difference in nuance.
I'm not sure exactly what you mean by the phrase "piracy is legends' vocation," i.e., How can legends have a vocation? And how does piracy relate to this? Can you please describe in more detail what you mean?
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