The early history of New World exploration reads like an old-style fantasy novel. Men from Europe literally traversed the North American continent looking for things like the City of Gold and the Fountain of Youth. With such a vast terrain ripe for discovery, there was really no way to prove those things couldn't be found, though not even someone as diligent as Juan Ponce de Leon was able to find any trace of such mystical destinations.
What they found instead was firm ground, mountains, jungles, rivers, deserts, exotic animals, and native inhabitants sometimes happy to greet them, sometimes happy to attack the newcomers. There are a lot of opinions and versions about the European exploration of North and South America, some of them accepted as standard, a few relegated to the conspiracy theorists' corner of shame, and one or two downright shocking.
Most historians agree that the initial Spanish and Portuguese insurgence, particularly in South and Central America, was occasioned primarily by greed and political jockeying. The big villain of this period was Hernan Cortes, a Spaniard who dealt freely in death, communicable disease, treachery, and gold between the Aztec empire and his own nation. It was said he pilfered so much gold his ships sank under it on the return journey.
Christopher Columbus has fared slightly better in the annals of history, though even his methods and motivations have fallen under suspicion. That he claimed the work of a missionary is now seen more as a burden for the Christian community to explain than as a noble mark in his favor. He also took gold, swapped diseases with the Indians, and provoked many to combat.
So what's the truth of all this? Are Europeans just a bunch of terrible people out to exploit everyone else? Is this merely liberal revisionism? The truth (as usual) is probably somewhere in between. Many of the explorers were pretty ruthless, but then again, the kind of personality that could accomplish something as arduous as the years-long journey to an unknown part of the world is bound to have some equally heroic flaws.