I join my colleagues and will overlap with them a little, but will take a somewhat different focus and tack.
Linguistis are interested in LANGUAGE which we investigate by investigating particular languages to find out how they work. Linguistics is about the actual form of language. It may be only about that, or it may be about that in possible variation with extralinguistic social and cultural or even psychological considerations. But it is about the formof language.
Linguistics is notabout any of the following:
a. social movements,
b. World Peace
c. Mutual International "Understanding".
In fact, Lingistics really isn't even about "communication", whatever that term might mean.
I actually studied -- no, investigated Esperanto in my youth, not to learn the language, but to find out how it works. That's the reason most linguists, especially linguistic typologists, study most languages they study.
But in Linguistic Typology we take samples of languages and we want to discover and formulate general "laws" of lingauage patterns. How in our sample do we count Esperanto? As Indoeuropean? As a very divergent Romance language? Or not at all since it was fabricated, continues to be fabricated, and will skew the sample.?
Moreover, Esperanto has an odd vocabulary mixture. Its roots are overwhelmingly Germanic and Romance. The author of the article you refer us to, Claude Piron, says in that article that "Esperanto's structures make it a non-Indo-European [sic] language". (page 11). He is flat out mistaken and shows that he doesn't understand historical-comparative linguistics. We do not determine language family membership by comparative grammatical structure but by the presence of regular sound~meaning correspondences. English father ~ Latin pater, Old Irish athair::English and German fish, Latin piscis, Gaelic iasg Welsh ysg. The last is the name of a river in Wales -- the ordinary Welsh word is pysgod., showing it to have been borrowed from Latin. Now, Esperanto is full of what are clearly Indoeuropean, mostly Germanic and Romance, roots -- but there are few patterns of sound correspondences -- suggesting the possibility of a very widespread pidgin lingua franca. Or suggesting the possibility that it was fabricated as a joke -- or, since we actually do know the historical context (despite what Piron alleges in his article you gave us the URL to), that it was fabricated for a Movement. Moreover, the common word in Esperanto for the most common coordinate conjunction is kai -- from the Greek word. But there are very very few other Balkan traces in Esperanto -- and it is very unlikely that a real pidgin would have done that. A language for pigeons maybe. But pidgins grow out of real interaction among real people in ordinary situations of contact. They don't grow out of highly fabricated conscious planning and continue only in highly controlled environments.
Furthermore, Esperanto in its structure and word derivation processes behaves very unlike any other pidgin I am familiar with. Pidgins do not have these elaborate derivational processes and many different derivational morphemes. As pidgins creolize, i.e. become fully fledged languages, they develop them. But they dont have them at the outset. Mouns end in -o but the article is la -- Zammenhof had sort of "draw them out of a hat" notion of what it meant to be "fair" and "neutral" in glomming together a language. In odd distribution of sources of vocabulary and odd grammar, Esperanto has a glommed together and overly fabricated look -- which is of course what it is. Therefore I as a linguistic typologist interested in formulating general laws about language cannot use it in my samples. Nor can I use Klingon.
But Claude Piron and the other Esperantevangelists say that linguists shouldnt deal only with the form. We should take into account the movement and the "world language problem" Esperanto was meant to solve. (page 24). Prion then does a pop psychoanalysis of linguists who dont do this and brands us as infantile in our thinking. That's like telling a chemist that he cannot study the combining properties of Sodium and Chlorine without taking cooking and heart disease into account, and that he is infantile for his "lack of inclusion" (page 24). This is passing silly and is one reason why real linguists, however much we may be interested in Esperanto, are not very interested in Esperantovangelists. Linguistics is no more about social movements than Chemistry is about how much salt to use in cooking. Or than banking and international currency systems are about coin collecting.
In your query, you give some thoughtful linguistic considerations (as well as social ones) about why linguists might be interested in Esperanto. I have tried to address a few of them here. But most Esperantians don't really want us to investigate Esperanto. They want us to promote it. Even neutrality raises their righteous indignation. We should stop doing what ever it is we do and start promoting Esperanto in the interests of World Peace, International Understanding, and "communication", whatever that is. I.e. we should stop doing linguistics and start doing something else -- or at least start using linguistics to do something else, that thing else being promoting their Faith.
Very few linguists are actually hostile to Esperanto -- being hostile to parents' making it their childrens' only native language is another matter. But what really gets to the Esperantovangelists is our I>indifferenceto it. And comments by linguists tend to be met with barrages of almost hysterical imagined counter arguments, most of which have relatively little to do with language.
Mr. Piron, whom you cite and directed us to, is one of the saner and more reasoned and articulate Esperantovangelists. Moreover, he appears to be an honest man. In his article, he included an appendix that gives at length many of the comments I and other panelists have published on this site about Esperanto. Now, you read those comments in his appendix, and thenreread Piron's article about them. What do you think now?
U of Cincinnati
Dept of Anthropology