My interpretation is that there’s a lot of dogma around how Japanese “should” be learned, in particularly among the English-speaking community. This dogma includes things like “you must learn kana first”, so a romaji-centered article triggered the alarm bells. Then there’s the general distrust of crank-style “beginner discovers the universe and wants to teach everyone” which also has a flavor of “he doesn’t understand that the only true way to achieve fluency is talking to people” and so on. It hit all the common warning flags that set people off, and that emotional reaction is the backbone of the response. It’s not an unfamiliar dynamic, and it’s reminiscent of some programming subcommunities, although in programming this dogmatic “you must learn/teach things this way” norm was more common in 2000s, and has mostly subsided by the end of 2010s. Overall, I get the impression that for a lot of people the difficulty of learning the language, and in particularly the difficulty of teaching it to others, have led to this kind of conviction. Once you’re expressing this kind of righteous rejection, I think it can be tricky to see that it comes across as sneering and gatekeeping when seen from outside your community.