While I upvoted the write-up, I would not call this mindset ignorant, nor, for that matter a mindset.
It is nothing specific to teenagers of today. I remember seeing an illustrated encyclopedia of social psychology during my psychology studies in the 1970's. It had a photograph of a huge crowd of sixites' non-conformists, all sitting the same way on some grassy spot, all dressed the same, all having the same body language, all conforming to the same type of non-conformism.
Being against norms is an important and essential part of growing up. Indeed, I would be worried about any teenager who does not rebel against the norm in some way (preferably without hurting or getting hurt).
The teens are a very difficult part of human life, but also very fascinating. It is the time when the young man or woman realizes for the first time that everything is not black and white. Until then, as a child, he/she accepted everything told by adults as absolute truth.
The teen now sees the relativity of much of reality. Yet, the teen is still not an adult. One moment he still acts like the child he was not long ago. Another moment he acts in a very mature way. He is torn between two identities: He is both a child and an adult, yet he is neither. He also feels that it is he against the world. He feels that no one understands him. In reality, it is he that does not understand himself.
Most adults know quite well what turmoil the teen is going through. After all, they once went through it themselves (though, some adults like to pretend they skipped the teens--they are most likely those whose own turmoil was above average).
Feeling that no one understands them, and being unsure of themselves, the teens then tend to group with and imitate other teenagers. Though they will never admit to it (at least not openly), they do realize that the other teenagers go through the same tough times as they do.
Unlike many adults I really love teenagers, especially when talking to them one-on-one (that is when they do not have to pretend they enjoy talking with someone "old"). Teenagers have very inquisitive minds, they're willing to totally accept an idea one day, then completely reject it another: How many adults do you know that are willing to do that?
When I was a teenager (back in the 1960's), I read an idea in a teen magazine. It said something along the line that if it feels like adults don't like to deal with you, remember it when you are an adult. Right then I decided I would never forget how hard it was, which is probably the main reason I still can have a very positive relationship with teenagers more than thirty years later: I treat them as my equals, not because I think it is somehow "politically correct," but because I think they are my equals. And I have kept my own inquisitive mind and the same openness to new ideas I had as a teenager. I do not swing from one idea to its opposite every day, mind you, but I have no problem with changing my mind when it comes to it. As an example, I was able to change my religion at the age of forty.
So, if any teenager who reads this is willing to take some advice from someone "old," my advice is: Never forget how it was when you were a teenager, and never lose your ability to change your mind.