because the article doesn't really support that. when you said "article that shows how America is still THE land of opportunity", you imply that this article shows that America has unparalleled economic mobility. The article doesn't support that conclusion. Then you say "well uh, I don't really know the subject, you should email the author". Instead of making a counter-argument (like "well actually, this evidence from the article shows it to be true", and then citing some evidence), you just fall back on a statement from the article. If you don't understand it in the first place, don't try to pretend like you do. Do you believe everything you read?

Just because the article has this line in it:
"Yet, in broad terms, the idea that America is a land of opportunity still stands", doesn't mean the article actually supports that conclusion. So next time you wanna say "yea, what's your point" or "did you actually read the article?", make sure you yourself understand it and what it's really saying first.