Not Saying Hello or Greeting People on Tishah b'Av

(I could've entitled this blog posting "You had me at not saying hello", although that would not be original.)
(Totally, btw, Havel Havelim #177: The Tisha B'Av Edition is out, with a link to one of my recent blogposts.)
I had started to look into the topic of not greeting people on Tishah b'Av on Sunday, but then abandoned it until I saw that Rabbi Ari Enkin wrote today on the same topic and I thought that I would add to the discussion [what I was planning on posting, pretty much, with some stuff in response to Rabbi Enkin's posting]. My main direction was going to be that the action forbidden on Tishah b'Av is שאילת שלום - inquiring into one's wellbeing and that saying "hello" should be okay, since they are different.
Why is it that on Tishah b'Av Jews are not supposed to greet people? Yes, as noted elsewhere, this custom "is rooted in the Laws of Mourning, because on Tisha B’Av we observe many of the same laws and customs that apply to a mourner." However, what I'm asking is how did this come about / why?
So before we actually get to answering this question, we first need to see what came before. We're going to start with Rabbi Yosef Karo's work, the Shulhan Arukh (או"ח תקנד:כ):

אין שאלת שלום לחבירו בת"ב, והדיוטות שאינם יודעים ונותנים שלום, משיבים להם בשפה רפה ובכובד ראש

There is no inquiry of wellbeing of one's fellow on Tishah b'Av. And simple people who know not and greet - we respond to them with a weak lip and with seriousness.

The phrase that Rabbi Karo uses here (שאלת שלום - inquiry of wellbeing) is one that goes way back, going back to Talmudic times of something that is not to be done. However, the question is what exactly constitutes this action from which people are to refrain? At face value, it would seem that inquiring of how one is doing is a problem but not simply greeting someone. At this point, it would seem that this could, as Rabbi Enkin wrote, "include the saying of 'good morning' or 'hello' in the prohibition of Sheilat Shalom, it is not entirely clear if such a greeting was intended to be included in the prohibition."
Rabbi Enkin references what Rabbi Zechariah Mendel (son of Aryeh Leib) of Cracow in the 18th century wrote (באר היטב יו"ד שפה:ב) on this topic:

אפשר לומר כיון שרוב שאילת שלום שלנו אינו אלא שאומר צפרא טבא וזה מותר שאינו שאילת שלום ממש כדאיתא בבית יוסף בא"ח סימן פ"ט והביאו בש"ע שם. ועוד מביא בב"י שם בשם ר"י פרישת שלום כמו כריעה אבל שלום בפה מותר כמו צפרא דמרי טב וכיוצא בו ע"ש. וכתב שם בד"מ דבזוהר פקודי דף ק"ג ע"א משמע דאינו אסור רק כשמזכיר השם וזה שם לענין שלא יתן שלום לחבירו קודם שיתפלל וש"מ שכל זה שאנו נוהגין אינו בכלל שאילת שלום כנ"ל

It is possible to say that since most of our inquiry of wellbeing is simply just saying "Good morning" and this is permissible that it is not really inquiry of wellbeing, as Rabbi Yosef Karo wrote in his Beit Yosef (OH §89) and he wrote this there in his Shulhan Arukh. And furthermore, he mentioned there in his Beit Yosef in the name of Rabbenu Yeruham that extending a greeting is like bowing, but saying hello is permissible, like "Good morning, sir" and other similar things - see there. And Rabbi Moshe Isserles wrote in his Darkhei Moshe that in the Zohar it is inferable that it is only forbidden when one mentions God's name (Pekudei pg. 103a). And this there is referring to the topic of not saying hello to one's fellow before praying. And infer from this that all of this that we are accustomed is not in the category of inquiry of wellbeing, as it seems to me.

An excellent summary of Rabbi Zechariah Mendel's words by Rabbi Enkin is that "[o]ffering another Jew a 'Shalom Aleichem' is more of a religious act than a greeting. Common expressions of 'hello', 'good morning', and the like, are simply not in the same league as is 'Shalom Aleichem' in neither depth, structure, nor status." While this is very logical and sounds nice, there are other positions in Jewish thought through the ages.
Rabbi Eliyahu Shapira wrote (אליה רבה סימן תקנד) in the century prior to Rabbi Mendel, starting off quoting[/paraphrasing a little of] what Rabbi Avraham Gombiner wrote:

כתב ביו"ד סי' שפ"ה יש אומרים דזה מה שאנו נותנין שלום לא מיקרי שאלת שלום שבימיהם, וצ"ע הא בטור כתב שלום עליכם וגם בגמרא אמרינן שלום עליך רבי, ולכן אין להקל (מג"א ס"ק כא). ולענ"ד כוונת רמ"א על צפרא דמריה טב דנהיגין האידנא, דלא מיקרי שאלת שלום וכמ"ש לעיל סי' פ"ט [ס"ב]. גם נ"ל דבט' באב הכל אסור, דלא עדיף מאבל תוך ל' דהכל אסור.

"Rabbi Moshe Isserles wrote 'There are those who say that when we give greetings to each other it is not called 'inquiry of wellbeing' that was in Talmudic times' and there needs to be further looking into the matter." Behold, in the Tur, [Rabbi Ya'akov, son of Asher] wrote "peace be upon you". And also in the Talmud, it says "Peace be upon you, Rebbe". Therefore, one should not be lenient." But in my humble opinion, Rabbi Isserles' intention was about saying "Good morning, sir" which we do nowadays, which is not called inquiry into wellbeing and as is written above in Shulhan Arukh, §89. It also seems to me that on Tishah b'Av, everything is forbidden, since it is not better than a mourner who is within the first month of their mourning, that everything is forbidden.

Furthermore, Rabbi Yechiel Michel Epstein wrote (ערוך השולחן או"ח תקנד:יח) a little over a century ago:

שאילת שלום אסור בט"ב דאינו יום של שלום כמו באבל כמ"ש ביו"ד סי' שפ"ה ושם י"א דשאילת שלום שלנו לא מקרי שאילת שלום אבל מהירושלמי שהביא הטור שם משמע להדיא דאמירת שלום עליכם הוה שאילת שלום ולכן אין להקל [מג"א סקכ"א] והדיוטות שאינם יודעים הדין ונותנים שלום מחזירים להם בשפה רפה ובכובד ראש אבל שלא להשיבו כלל אין נכון כדי שלא יתבייש וכן אין לילך ולטייל בט"ב בשוק וברחוב דהטיול בעצמו אסור בט"ב ... וכן לומר בט"ב צפרא דמרי טב ובלשונינו גו"ט מארגי"ן אין לומר בת"ב

Inquiry into wellbeing is forbidden on Tishah b'Av, since it is not a day of wellbeing, like a mourner (as is written in YD §385). And there, there are those who say that our inquiry of wellbeing is not called inquiry of wellbeing, but from what Rabbi Ya'akov ben Asher wrote in the Tur, quoting the Yerushalmi, it is explicitly inferable that saying "peace be upon you" is inquiry of wellbeing. And therefore, one should not be lenient. And common people who do not know this rule and greet you, we return to them with a weak lip and with seriousness, but it is not proper to not respond at all, in order to not embarrass them. And thus, one should not walk and wander about in the marketplace or in the public square on Tishah b'Av, since just walking about on Tishah b'Av is forbidden. ... And thus, one should not say "Good morning, sir" (or "Good morning" in Yiddish) on Tishah b'Av.

In any event, I'd like to agree with what Rabbi Enkin suggests that

it seems quite reasonable that using God's name when in mourning may be inappropriate, saying "hello" should be no worse than any of the other mundane conversation which take place on Tisha B'av, or in a house or mourning, for that matter. When one picks up the telephone the first word is always a "hello" which is not truly a greeting at all, but rather an expression of readiness to engage in conversation. There is no prohibition on conversation on Tisha B'av or in a house of mourning.

Rabbi Enkin concludes by suggesting that although there are those who may follow the opinions that are not so okay with greeting (such as we saw with Rabbi Shapira and Rabbi Epstein) that "it cannot be suggested that a simple social acknowledgment is in violation of halacha. Those who feel that it is rude or uncomfortable to pass others without an acknowledgment of some sort should feel free to offer a somber 'hello' without reservation."