[cam-stitt]

The article is titled "I Don't Believe in Full-Stack Engineering", yet states "If you’re only hiring full-stack engineers" as though they are something the author believes exist.

It seems that the real approach of this article should have been to outline why hiring ONLY full-stack engineers may not be a good idea.

[jfz]

The author probably meant that they don't believe that full-stack engineering is beneficial compared to hiring primarily specialists.

[cam-stitt]

Potentially. Which is why I believe that it is more of a click-bait title than a meaningful discussion point.

[pseudalopex]

It's a common idiom. Someone who says "I don't believe in psychics" means "people who call themselves psychics don't have the abilities that implies", not that nobody claims to be one.