Who are generally the most close-minded fans?

My thoughts always were that when someone did not enjoy something and were (what we call) close minded about it, the issue would then be that such a person might not exactly be a music lover .... if you are a music lover, you might not exactly prefer this or that, but you will always appreciate the musicianship and the care it takes in putting it together, specially when it takes several folks.

But, there are other reasons which are hard to include/not-include here, and the most common one is the singing in a different language. Many folks don't like ANGE because of the very romantic (classical romantic and very french) style of singing, not to mention its acting component, which has a massive history in French music. A lot can be said for the Italian bands as well ... I still prefer PFM's original albums, Banco's original albums, and even Le  Orme's original Felona e Serona ... there is a feeling of honesty and emotion that does not translate as well with different words in different languages. To me, this is like listening to Verdi, Puccini and many other operas ... they teach you how to feel and understand a lot of the music behind it.

For me, these are not a problem due to the fact that I was born into the Latin Bloc of languages, and there are many things in the grammar in them that are similar making the understanding of it very different from a translation. Translation, based on what has happened on my father's work is ... I want to say CRAP, because sometimes folks like to invent a socio/political idea that is not exactly there in the original, and if it is, it is subtle and not a part of the "forefront" of the words, or ideas.  My dad did not live "in fear" if his politics were open and heard, but there had been enough problems and political deaths in the family to consider being quiet and not spend the time teasing, or creating situations that could easily be understood and taken badly ... that would, likely, involve family members being taken away! Thus at times his work comes off as completely personal, and not socio/political at all. Again, however, some translations have gone too far ... including one that is boring ... that suggests that because the character has a red sh*t on that it means ___ such and such ... and c'mon, it destroys the story in my book. It didn't need that idea or comment.

And this is the hard part of the romance languages (the Latin bloc), since there are verb tenses that have an expression that does not translate well into English at all and I get caught in these a lot ... "stop making assumptions" ... it's not an assumption as much as it would be a what if, a verb tense that doesn't exist in English and is often translated badly, and some folks here, always take it personally, because I'm not sure they are reading the whole paragraph, or sentence, but that might be up to discussion ... i real life, I do not spend any of my time insulting anyone and in fact, I'm a bit on the crazy side ... I talk to all the little animals in my yard, feed them, and they respond too! Some even come to my hand!

Music for me, just like the arts, is the best the universe in this earth can show us ... there are no other words for it, and I find it weird when folks think I'm intentionally pointing at someone or something, although I tend to use a lot of Goon humor on it ... which some folks don't like, I found ... they are not "imaginalists" like you needed to be for old radio and music with a foreign language at the front.

Which, might be the real issue ... because for me even Japanese or Chinese comes alive in my head. It doesn't even matter what it says ... I learned that quickly with Sadistic Mika Band ... it was wonderful!

But then, who are the most open-minded of music listeners? Avant-RIO?

For many years I was a very closed minded fan, even though I came from being a new wave and hard rock fan in the 80's, however I got into prog at age 13-14 by my early 20's, I did not listen to anything but prog or jazz ( love ECM and traditional Jazz). I was extremely hatefully for everything else!. them I got into Dream Theater, Symphony X, Meshuggah, Fate Warning due to the progressive rock reference them I started listening to Death, Thrash and Symphony Metal bands. I still can't get into Black Metal unless it is a mix of Doom and Symphony Black Metal. I can't listen to the singers. Again in the late 90's early 2000 I started getting into Post punk and alternative bands like the Smiths, The cure, The church. 

 I don't know I just feel that it has helped to appreciate and respect all time of rock and music in general. Prog is still my favorite however, but I like to give a chance to music that is  simpler and easy listening and has nothing to do with prog. 

 disagree! most prog fans  specially old fans of prog bands from 1969 to 1980. THEY ARE VERY OBNOXIOUS. 

The first paragraph is so spot on I will applaud you 

The stuff about foreign language. Well I can only speak for myself but I would also rather bands sung in their own language. I was not always aware of this even being a thing though. I had no mentor to show me the way and to explain to me that PFM's original albums are so wonderful. I know this now. My first inkling of the potential and power of using one's native tongue was Anglagard's Hybris album. I still much prefer this to the other 2 albums they released which I think were mainly intrumental. I now listen to quite a lot of prog with non English singing. Bring it on!