If people are learning English on Duolingo, I wonder why there is no English discussion section. Some of us have experience helping foreign students learn English.
We do have a discussion board in each language, but they are all separated. Much like this discussion board is entirely in English, the discussion board of people learning English from Spanish is entirely in Spanish, the one of people learning English from Portuguese is entirely in Portuguese, etc. We believe that having all boards in one would create language chaos :)
Duolingo of course will set its own policies. But I don't see what is so bad about getting a lot of comments from English speakers if one is trying to learn English. The comments will usually be in English (not always) and that may confuse some students, but that's not a huge problem. I have certainly seen it work successfully elsewhere. Many students enjoy communicating with English speakers in English. And it's certainly true that some native English speakers are not good teachers of English. Some Spanish speakers are also not good teachers of English. All the better to get a lot of comments.
There actually is an English discussion, but it doesn't seem to be visible to those using English to learn a different language. I peek at the English discussion by following someone who comments on it. My guess is that he switches back and forth from English to Spanish and Spanish to English.
My guess is that Duolingo is trying to avoid confusion. In other words, typically, the Spanish to English board is predominantly in Spanish, and if it was easy to reach, I would guess that it could be inundated with English which would defeat its purpose.
Though, honestly, I've learned an awful lot by sneaking onto the Spanish to English board.
Also, keep in mind, that just because one is a native speaker of a language that doesn't necessarily make one a good teacher of the language.