Thus to get my (and the article's) point, you need not just stop teaching it to children, you have to completely erase the underlying knowledge the language holds and start over in a new language. This is the point: you lose much more than what appears on first glance.
And concerning programming languages, I don't see how picking up brainfuck for example is easy, but someone still put the effort into creating it. Imagine a universe in which you'd have to solve every single programming problem in C. You could dream up all sorts of programming language concepts, but you could never use any other language than C. I bet you'd find that a bit boring and tedious...
Make no mistake, I'm not advocating for languages to keep their purity. I think it's a good thing they mix and borrow concepts and words. But I do find the idea of having one world language an utter absurdity.
'Please don't insinuate that someone hasn't read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that."'
Only if you stay in the same family. Going from C to C++, Java, or C# is pretty easy. Try going from C to Haskell or Clojure or Erlang.
You can play the same game with natural languages. It's easy to go between French, Italian, and Spanish. Try going from Icelandic to Mandarin.
By contrast, we can easily install the same version of a programming language interpreter/compiler and run-time onto countless machines and get the same behavior. The machines do not have to guess what the language is by forming hypotheses and testing them against more competent "speakers", to obtain either approval or correction. They just receive a ready-made software image.
In essence, a million installations of the same programming language are just manifestations of one image, whereas a million speakers of a language are individuals (not just as people, but as speakers of that language).
If people could receive a language as an image dumped into the brain, it would be a game-changer. It would still be a game changer even if it took five years to complete, rather than an hour. It would make fledgling languages more viable.
Because languages are hard to learn and even harder to learn very well, people tend not to be so interested in fledgling languages that can't be used outside of a small locale with a small number of speakers. Not as a second language, that's for sure.
I'm not comfortable with the idea that something which pops into my head today represents a burden for future generations to preserve, who will have perfectly good heads of their own into which similar stuff can pop just as well.
Linguists require specimens of languages to study so that we can understand language. But we have more than enough non-dying languages to keep linguists busy.
1. They're not that different. Once you've learned a few, picking up new ones is pretty easy.
2. They're much easier to learn than human languages.
To answer your first question: I probably wouldn't stop using english myself, but I don't think I'd teach it to my children.