Although I don't believe that you finished reading the article -- that's not what "this guy" is saying ... you are raising an extremely good question.

Part of the answer is explained by JavaScript's inherent popularity as the language of the web -- everyone has something at stake, when JavaScript is involved. To paraphrase myself from a similar thread last month:

Most esoteric programming languages are non-threatening. As a hypothetical programmer working on web applications, I can feel safe and comfortable in my ignorance of Haskell, Erlang, D, Io, Arc, and so on. They're far enough outside of the realm of possibility of adoption for my company that I can shrug them off with an "oh, that sounds interesting", and little more. Wanting to adopt one of them would require a whole new development and deployment stack, a new or ported codebase, and new integration costs with the rest of our system. You wouldn't expect to see an article talking about how people using Erlang are creating a "knowledge gap" for Java programmers.

CoffeeScript feels threatening precisely because it is so close to JavaScript, because the code can run with identical performance as hand-optimized JS anywhere that JavaScript can run, because any CoffeeScript library can interoperate seamlessly with any JavaScript library, and vice versa. It forces you, as a reasonable JavaScript programmer, to answer the harder question: Why should you be limited to a language that hasn't changed (IE6/IE7) since 2001?

I personally write stuff like this because the act of writing out my thoughts forces me to think them through clearly. In this case, I actually do agree that CoffeeScript is a “little” language, but writing an essay in this form was an exercise in clarifying what is and isn’t a language and what that means.

Other reasons for writing essays to convince people to use or not use a language like CoffeeScript might include a very natural desire to get lots of people using the tools you prefer. If you prefer JS, but everyone else write cool stuff (like Katy!) in CS, you will be annoyed trying to read their code or step through it in your debugger.

Conversely, if you prefer CS, getting momentum behind it ensures its future and increases the probability you will still be able to use it in the future.

I can certainly appreciate why people might want to evangelize either position. For me, it was an exercise in taking an interesting position—that it’s about the JavaScript it generates not the grammar or syntax—and see if I could make a credible argument.