Actually, Stark brought Parker across international borders without a passport or consent by his legal guardian, engaged him in an attempt to arrest a “war criminal” and a cybernetically-enhanced Hydra superassassin, and participated in vandalism and destruction of a public airport. Short of handing him a beer and a joint and leaving a couple of prostitutes in his room to “give him a massage”, Stark basically checked the “corruption of a minor” checklist.
Yeah, that’s certainly true, and to a large extent you just have to suspend disbelief when watching these movies. But that doesn’t mean it isn’t fun to discuss how Professor X is actually creating a death force of teenagers with dangerously unstable powers led by a guy whose primary attributes are constantly smoking cigars and going on an animalistic rampage, killing everyone in sight with giant concealed claws. And that doesn’t even get into the whole ‘Dark Phoenix’ issue.
I had a point when I began this, but it has since left the planet and gone to fight on the other side of the galaxy for the entertainment of immortal beings of immense power and knowledge who have nothing better to do than oversee gladiator tournaments.
It did happen just a couple days before Stark’s killbot decided to drop Sokovia on the world. So it’s not surprising it got pushed below the fold. And Hulk, who was really responsible for most of the damage, went M.I.A. and ended up across the galaxy, so that particular problem took care of itself, or at least became someone else’s issue to deal with.
Lots of good arguments here, but I think the universe of comics just considers superheroes to not follow the usual rules of child vs. adult. Spiderman actually addresses this issue frequently. Spiderman is an experienced superhero who had better than average judgment even when he started out. He acts like an adult, constantly second guessing and analyzing his own actions. When he encounters other wannabe superheroes, he discourages them if he feels they are reckless and not ready. Even superheroes much older than him, he will get into scuffles with if he doesn’t like their tactics. His first battle with Wolverine is a classic, and Wolverine is one of the most mature superheroes in the Marvel universe, although he’s also got serious mental issues.
So the movie is set in a universe where even though Peter Parker is young, he’s proven he can handle the burden. And if there’s one thing superhero comics and TV shows will tell you, it’s that you can’t stop young superheroes from superheroing. This would be true in real life as well. If you can save people, and you’re 10 years old, you’re going to try to save people. Stark just figured that a) Peter had proven his trustworthiness, although Stark still felt he needed watching and guidance, and b) the mission was very limited, and while dangerous, the chance of death or serious injury was tiny. This proved to be erroneus, although Peter wasn’t the victim in that fight. Tony’s best friend was.
Was he really responsible? he was mind fucked by Scarlet Witch, kinda hard to blame him. Yeah, the Hulk is dangerous but if someone hacked one of Starks suits and went to town on a city with it most if not all of the blame would go to the hacker.
In regards to the Hulk, he didn’t make the hackable superweapon and not having Hulk in the Avengers doesn’t make anyone safer. Other methods of stopping the Hulk have been tried and they always fail. Better to have him around other superheroes where they can dogpile him when he gets out of control then to have him roaming the countryside like he did getting into trouble like he did for the first 30 years of his comic run.