But Lag B'Omer is an odd day to celebrate, I think. Yes, the talmidim of Rebbi Akiva stopped dying on that day. The reason they stopped dying is because every last one of them was dead. There was nobody left to die. This we celebrate? The famous talmidim of Rebbi Akiva that we know of were those that he taught after all the others had died.
As for the "Hilula of Rav Shimon bar Yochai" that is mentioned in the Zohar- that, too, is difficult to understand. If it is the yahrtzeit of Rav Shimon bar Yochai, the day of the death of a tzadik is not the time to make a party. On the contrary; there are many Gemaros that say that one should fast and mourn on the anniversary of a Tzadik's death: the suggested fast days we know of are the seventh of Adar, for Moshe Rabbeinu, Rosh Chodesh Nissan for Nadav and Avihu, the tenth of Nissan for Miriam, and so on. So why are we celebrating on the day of Rav Shimon bar Yochai's death?
The Zohar that calls it a "hilula" means something else entirely. Although the day of a tzadik's death is a day of Middas Hadin, a day of sadness and introspection for the treasure we lost, that is only on Earth. In Shamayim, it is a day of rejoicing, like a day a Kallah is brought to her Chassan. In Shamayim, it's a Yom Tov, a mo'eid of Hillula. On Earth, among the living, it may be a mo'ed, but it's a mo'eid like Tisha Ba'av.
I understand that what I've written seems disingenuous, and seems to denigrate a holy minhag that has existed perhaps for millennia, certainly for hundreds of years. As for what I said about their not dying anymore because they were all dead, well, it's no different than the fifteenth of Av, when the generation of the Midbar stopped dying because they, too, were all dead, but we celebrate the end of the gzeira ra'ah. Also, at least Rebbi Akiva remained alive, and he ultimately managed to teach his Torah to other talmidim. As for Rav Shimon bar Yochai's death being a sad loss for mankind, but we are all told that on the day of his death he revealed many secrets of Toras Hanistar to us, so it's like the day of Mattan Torah of Toras Nistar.
In defense of my seemingly "haskoolisheh" post, I would like to point out that nothing that I've written originated with me. Everything I wrote is lifted- almost verbatim- from (second paragraph) the Pri Chadash in OC 493:2, and (paragraphs three and four) from the Chasam Sofer in Parsha Emor. They are the ones who disapproved of the party atmosphere of Lag Ba'omer and the mass gathering in Tzfas, not me.
The Chasam Sofer's words were written in a eulogy he delivered upon hearing of the disastrous Earthquake of the Galilee that occurred on Sunday January 1, 1837- 24 Teves, 5997. That earthquake hit Tveria and Shchem and destroyed most of the Jewish section of Tzfas, leaving thousands of Jews dead; adding insult to injury, it barely touched the Arab section. The Jewish community of Tzfas, destitute even before the earthquake, was decimated, dislocated, and plagued by injury, infection, and disease. The Chasam Sofer suggests that this was divine punishment visited upon us for ignoring Yerushalayim. He says that for around one hundred years prior to that date, nobody wanted to live in Yerushalayim, but instead everyone went to Tzfas to be in the proximity of Rav Shimon bar Yochai's grave. He says this was a terrible insult to Yerushalayim, the Gate of Heaven, the source of all Kedusha. He brings from the Ya'avetz that even now there is a mitzvah of Aliya le'Regel, (though I haven't found the teshuva he's referring to,) and we, as a people, were punished for insulting the kedusha and centrality of Yerushalayim.
Eli, in the comments, notes that "it was also found (in the Cairo Genizah) that in the times of the early Geonim, Iyar 18th was considered the yahrzeit of Yehoshua Bin-Nun, and, accordingly, a fast day." The Chasam Sofer in the above hesped says that Yehoshua bin Nun's yahrtzeit is the twenty sixth of Nissan, though.
So, if your Rosh Yeshiva tells you that you can't go dance in Miron because it's bittul Torah and hollelus, at least you know that while your Rosh Yeshiva won't win any popularity contests, he'll be unpopular together with the Pri Chadash, the Chasam Sofer, and the Geonim.
But in the end I have to admit that Lag B'Omer, whether it really has any intrinsic deep meaning or it's just fun, is certainly a good and healthy way to enjoy the achdus and spiritual aspirations of Klal Yisrael. Like many other good minhagim, you get out of it what you imbue into it. As George Bernard Shaw wrote,
I don't believe in circumstances. The people who get on in this world are the people who get up and look for the circumstances they want, and, if they can't find them, make them.
Le'shana haba'ah be'Uman!