I talked to an Australian magazine that will remain nameless where the executive on the other side of the table told me their business model was 100% sponsored content. I couldn't tell, from their website. Every single article was a sophisticated ad. He said they were doing fantastically and growing fast, users wanted that kind of stuff.
It reminds me of Ogilvy's book on advertising [1]; Ogilvy's experience taught him that informative ads that explained the advantages of the product were most successful with customers. Sponsored content is exactly that, and the opposite might be something like clickbait [2].
Sponsored articles are accessed voluntarily by the customer clicking on them and reading them, and returning to the site; they are unobstrusive being mostly made of text and of (relatively) higher editorial quality, with good photography and so on. I wonder if they are the future of advertising.
On the topic of being unable to filter advertorial content from, well, content, I don't think it's as clear cut as ads vs not-ads, since every writer has their own set of opinions and presents their world view only (with few exceptions). A necessary life skill is critical thinking, learning to dissect an argument, examine its assumptions and data, and come to an independent conclusion as to the point it is making.
[1] core principles are summarized in his "house ad": http://smartonlinesuccess.com/wp-content/uploads/2012/04/dav...
[2] famously (NSFW): http://www.lazygamer.net/general-news/a-history-of-evony-ads...