Menachem Kellner wrote a book on the topic, where he builds on work by Moshe Idel. Kellner takes for granted that Rambam rejected (what was taught as) kabbalah of his day, and his book 'shows' how much of the Rambam's writings were aimed at presenting an alternative to kabbalah. You could read his book as indirectly proving that the Rambam rejected kabbalah, ...
The Yosef Da'as on this section has a fascinating approach.
It seems that it was obvious to everybody that Ben Zoma had (somewhat) gone out of his mind (as per Rashi) from his super-spiritual experience.
Gemara: בן זומא הציץ ונפגע - Ben Zoma peeked and was injured
Rashi: ונפגע. נטרפה דעתו - Injured: his mind was jumbled (lit.)
The Rabbis then tried ...
This seems to be based on a misunderstanding of the Mishnah in Chagigah. Rashi explains "what is above" to mean:
מה למעלה - מרקיע שעל ראשי החיות:
Above the firmament which is above the heads of the Chayos
If Gehennom is below the Chayos but above the sky, there's no prohibition involved.
In a similar vein, the Maharsha on the spot understands this ...
The Gemara you quote asks and answers that very question.
Miriam B was doing something dangerous and thereby she was at high risk of dying.
היכי יכלת לה? הות נקיטא מתארא בידה והות קא שגרא ומחריא תנורא שקלתא ואנחתא אגבה דכרעה קדחא ואיתרע מזלה ואייתיתה
היכי יכלת לה. מאחר שלא הגיע זמנה: הות נקיטא מתארא בידה. היתה אוחזת בידה האוד של תנור ...
Chagigah 27a gives two explanations of the Sages' opinion:
They are actually arguing against R. Eliezer. They believe that the altars are susceptible to impurity, and are not viewed like the ground, because they are coated with metal.
They are saying the following to R. Eliezer: "Why do you need to compare the altars to the ground in order to render them ...
Shearim Mitzuyanim Bihalacha points out the interesting language concerning Torah 'from his mouth', why did the Gemara not simply say from him?
He quotes the introduction of the Darkei Teshuva to answer this, and I think it will answer your question as well.
Darkei Teshuva wrote: if the Rav says a halacha with proper proofs, then one can learn (be מקבל) ...
The Michtam L'Dovid, Berachos 2:8, in addressing a different question, writes that this Gemara is not an example of Hashem acting unjustly, because it wasn't Hashem who did it, but rather the Angel of Death - דמלאך המות הוא דעבד הכי, ולאו הקב"ה אמר לו להמיתו. This would then be an example of an angel making a mistake, not of Hashem being fast and loose ...
Rashi on the Mishna explains these to be talking about what seems to be a "spiritual" above and below.
מה למעלה - מרקיע שעל ראשי החיות:
ומה למטה - מהן:
What is above - from the "firmament" above the "chayos" (a type of Angel)
What is below - them
While enjoying and learning from Danny Schoemann's answer, I'd like to offer another route to understanding the idea that Ben Zoma went insane.
In describing the episode, the Talmud identifies the effect of Ben Zoma's experience in entering pardes with a particular biblical verse:
בן זומא הציץ ונפגע ועליו הכתוב אומר (משלי כה, טז) דבש מצאת אכול דייך פן ...
The first part of the quote from Acher was that which he held to be true until enter the pardes (i.e what he learned from his teachers). The second part is the conclusion he mistakenly drew based upon what his eyes beheld, which led to his excommunication/loss of heavenly reward.