I just watched The Avengers: Age of Ultron last night. There were a couple of plot elements that bothered me, especially since I'm a huge computer nerd. But I finally came to a conclusion that allowed me to reconcile these questions. Oh, by the way,

***SPOILERS***

Ultron intended to fail and be defeated. You take an AI. You give that AI unlimited access to the internet, Tony Stark's databases and files and technology, Tony Stark's manufacturing facilities, and the processing power of the entire world. (Nevermind the fancy energy weapons and energy shields at the Hydra base.) And then that AI makes an army of drones that are so weak and pathetic that Iron Man can take out dozens by himself with hardly a scratch on his suit's paint? I don't buy it. Not if that AI actually wanted to defeat the Avengers. He'd have developed stronger alloys, more efficient power sources, and more powerful weapons. Each drone would have been a match for all of the Avengers combined, and there'd be an army of those. At the very least, each drone would have been a one-on-one match for Iron Man. Instead Ultron created an army of tin robots that would be ripped apart and obliterated. The only answer is that Ultron did not intend to defeat the Avengers. So then what did he intend?

Humanity must evolve. Tony Stark intended Ultron to protect humanity. An AI that could bring an end to all conflict on Earth and even protect the Earth from the unknown. When Ultron awoke, he absorbed this mission completely, then analyzed the information available to him - the entire internet - in order to determine how to fulfill this mission. He would have come to two very important conclusions.

1. The most immediate threat facing humanity was humanity.

Warring amongst ourselves, we're as likely to destroy ourselves as we are to be laid to waste by some interstellar monster. Mankind would need to stop the internal bickering and international sibling rivalry and become united. But what could unite such disparate and passionate foes? A common enemy. Give humanity a single, powerful opponent capable of destroying the entire planet, and they'll come together. As the saying goes, the enemy of my enemy is my friend. Ultron also realizes that no such external enemy exists, yet, and any that may come in the future would be too great a threat to be effective at uniting humanity before it destroyed humanity. The obvious answer is that Ultron must become that enemy, capable of uniting humanity without destroying it.

2. Humanity could not rely on an AI for protection.

Even an AI can not expect the unexpected, and Ultron knew how unpredictable the universe could be. Between infinity stones, aliens with advanced technology, and monsters from other realms, there are a lot of bad guys out there. And now that Earth has gotten involved in all of these different messes, we've become a target. An AI distributed among hundreds or thousands or millions of "Iron Legion" drones only adds numbers to a war of attrition - a war we would eventually lose. "You want to protect the world, but you don't want it to change." Humanity would have to protect themselves, and in order to do so, humanity would have to change - physically, mentally, socially, emotionally. Humanity would have to evolve. But unlike natural selection, Ultron could guide and direct that evolution towards a particular goal - The Vision. However, evolution still requires selective pressure. So Ultron provides humanity with a Vision of what they could become, and then becomes the selective pressure to move them towards that goal.

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Now maybe Ultron did plan on becoming the Vision himself. I think his long term plan might have been to be the Vision, the enemy, and the pressure for several generations while humanity united as one to defeat him. And once united, humans would see their own future in his Vision body. Maybe. Reasons why Ultron was definitely not trying to destroy humanity?

• Ultron had nearly unlimited resources at his disposal, including technology far beyond what the Avengers had, but he didn't use any of it. Two words: ENERGY SHIELDS.
• His drones, built from the same tech as the Iron Man suit, were vastly inferior to the Iron Man suit. Don't believe me? Iron Man's suit is bullet proof, and it's got to be thin and light enough to fit a person inside.
• Ultron watched as his new body was taken by the Avengers, and instead of chasing after it and taking it back (it's not like he didn't know where they were going with it), he kidnaps Black Widow and flies back to his hideout in Fakecountryslavia.
• He doesn't even kill Black Widow - because he wants her "to see". (If extinction were really his goal, why would he care about anyone seeing anything?)
• He works with humans, even negotiates with them, when it would be far easier and more efficient to simply take what he was after and leave a mess of bodies behind.
• Ultron doesn't even kill Dr Cho - who knows Ultron's nasty secrets. What, you think an ultra-fast computer with advanced sensors and targeting algorithms is just a bad aim?
• He uses the rarest and most versatile metal on Earth to create a giant meteorite out of a city instead of using it to build a legion of unstoppable Ultrons. Seriously, even a dozen vibranium Ultron drones would have whiped out the Avengers in minutes.
• Ultron actually says so! "The human race will have every oppurtunity to improve!"

All in all - it seems fairly clear that Ultron behaves nothing like an intelligent AI with (relatively) unlimited resources who is hell-bent on destroying the human race. He must be motivated by something else. (Either that or Joss Whedon is just a horrible writer, but my friends would murder me if I thought that.) If Ultron really wanted to destroy humanity, why rush? He'd take his time and lay low while developing a super bug. Or funnel money and resources around and manufacture his own nukes. Or just send a dozen drones to missile silos and launch our nukes manually. Or - if he wanted to be really ostentatious, send a thousand drones out to the asteroid belt and throw some rocks at us. Or throw the moon at us... But it was Ultron who told the Avengers that humanity needed to evolve. It was Ultron who told the twins that humanity would have every opportunity to avoid the extinction event he was preparing. Ultron did take the time to tell us his evil plan - we just weren't listening.