I wouldn't be upset if he was allowed back, but it should definitely be on a "no more warnings" level.
As far as the number of views his videos have, I tend to dislike most of the popular youtube channels. Ever seen the most subscribed to Youtuber? PewDiePie? He is very similar to Adam in that he constantly makes "quirky" remarks and his entire shtick is to be "random". If you look at these guys fan pages, it is generally the tween/teen demographic that is consuming this stuff. So sure, they aren't OLD enough to trespass and vandalize because they can't go yet, unless they are with mom & dad, and that sort of makes it hard.
Now I get that I am generalizing here and that some of PewDiePie and Adam the Woo's fans are adults. People can enjoy whatever humor they want, that's not what I'm complaining about. But it is a fact that the MAJORITY of these youtube viewers are younger. So whether or not they grow up to try similar stunts is to be seen. Maybe they won't, but maybe they will. And maybe banning Adam will scare some of them into not attempting something that is illegal and could possibly end up injuring themselves.
The simple fact is, if Disney allows him to do this and doesn't step in, then they encourage others to do it. And others WILL do it. At one point an abandoned amusement park in El Paso, TX called Magic Landing became a popular destination for "urban explorers". For the first year or so the visitors were just taking pictures. But as websites featuring these pictures got more and more views, the type of people going became a lot more varied. Now people were actively stealing things. Others were lighting fires. Smashing things. Within 2 years the place had 3 or 4 reported fires and almost everything in the pictures originally taken had been destroyed or was stolen. Eventually the land owner had to demolish the entire site to prevent this behavior.
The EXACT same thing happened at the New Orleans Six Flags after Katrina. At first it was just urban explorers. Then vandals, arsonists, thieves, and all sorts of others showed up.
I have been following various urban explorer sites for over 10 years. Essentially, every time a location has become well known, it has become over run with people who destroy the site. As far as Adam goes, it starts with a person going into the Universal backlot because they loved Nickelodeon studios when they were a kid. They get excited when they see the old signs and paint jobs. They check door handles to see what is open and flip switches to see what is still on (Adam does this EVERY time he sees a switch, faucet, anything - he starts messing with it). At that point your messing with stuff that you may not fully understand how it works. Maybe you turn the faucet and nothing comes out now, but later maintenance turns the water on (assuming all the faucets are off) and that area starts flooding because the drainage is backed up after several years of neglect and they didn't realize that some suburban kid with a camcorder acting like a clown was turning faucets on and off in an effort to get hits on youtube. The fact is, he isn't just walking around looking - he is touching things and messing with things.
Eventually someone comes through that loved Nickelodeon (in this case example) so much that when they see something that isn't nailed down, they decide to take it as a souvenir. In their mind no one is using this stuff anyways, and it has meaning to them, so why not. It's not malicious, but it's still theft. As the number of visitors expands, eventually you get someone who can't get a door open so they start trying to kick it in. This behavior continues until things break, are stolen, or someone is hurt. In all three cases, Universal is losing something. Whether its property or money due to liability. This WILL happen because this ALWAYS happens when people are allowed into abandoned/closed places.
So no, it's not cool for Adam to do this. Because others WILL do it. Every single other abandoned location that people can get to goes down hill as soon as there isn't someone there to block people from entering. And in every single case, the more people who visit, the quicker the location is destroyed. In this case, both Disney and Universal are active entertainment spots for families with HUGE reputations to protect. They have even more to loose than some owner of an abandoned tract of land with a derelict park sitting on top of it.
If some kid gets backstage at Disney and hurts himself, Disney looses money. They loose money if the kids gets hurt because of liability. They loose money from lost visitors who think Disney isn't safe because they heard a biased report on their facebook page about Disney ALLOWING children to roam backstage, etc. You simply can not allow this type of behavior. The fact that I find Adam's sense of humor to be juvenile is completely unrelated. Even if he conducted himself like an adult and didn't feel the need to announce his activities like a spastic child, it would still go against everything I stated above to allow him to roam around back there with his camera.