[mindcrime]

At that instant I knew he had posted this link on Hacker News not to be informative, but to prey on developers with weak marketing skills, and get them to pay for his book.

OK, the fact that you would use a term like "prey on" in this context tells me that we probably have radically different worldviews, so there may be no point to this exchange, but...

I would say this is an unethical advertisement because it pretends to be an article, but it actually was an advertisement

There's no particular reason a piece of content can't be intended to be both legitimately informative, AND serve to drive awareness of something your selling. In this case, ask yourself this: If you took away the last paragraph or two of the article, would the rest of it still have been informative? Would you have gotten value from it? If so, how is it not an informative article, just because of the blurb tacked onto the end, sharing information about the author's book? Especially when the book is relevant to the audience who would likely discover that article?

OK, I get that a lot of developers just have a sort of general aversion to "all things commercial". Hell, I used to be that way to some extent, but yet I always found marketing fascinating, and now that I run a startup, I find marketing essential, so maybe my views have shifted a bit. Anyway, I understand - to a point - that a lot of us find that commercial interests take away from some notion of essential "purity" or whatever when it comes to technical content. But to call this kind of content marketing "unethical" is a bit extreme, IMO.

[tbirdz]

If it has value on its own without the paragraphs about buying his book, surely it would have just as much value if the author moved the final paragraphs to the front, and clearly identified it as an advertisement for his book. The fact that he did not do that indicates that he thought less people would read it if they knew it was an advertisement right from the start. So then the author thought he would have to trick people if he wanted to get them to read the advertisement, so he sneaked it in at the end. This intent to deceive is what I am calling unethical. Now, sure this could be an effective technique, but the kind of deceit and trickery usually involved in such marketing leaves me with a bad taste.

[mindcrime]

The point is, there isn't a binary distinction between "it's an advertisement" and "it's informative content". It's a legitimately informative and interesting article, whether or not he mentions his book. So what difference does it make if he mentions the book at the beginning, or the end, or not at all?

And putting that stuff at the bottom has nothing to do with being tricky, or sneaky, or unethical. It just makes more sense to mention the book after the author has demonstrated some credibility through the content in the earlier part of the article.

[verisimilidude]

The message, whether informative, promotional, or both, ultimately needs to reach its audience. On both counts, this article failed to reach tbirdz and likely many others.

It wouldn't have been too much trouble to bring those skeptics back to the conversation by adding a short disclaimer closer to the beginning of the article. So why not do it? If the article is going to be both informative and promotional, some will want that expectation to be set right from the beginning. And if the informative bits can stand on their own merit, there's no risk to the promotional side in adding the early disclaimer. (IMO, it's not an unreasonable request, and not without precedent.)