What I am trying to say is not that belief in gilgul neshamos should be an ikkur today, but that there needs to be acceptance by the individual of those ideas that were accepted by the greater majority of the previous generations of gedolim.
To illustrate this point. I have seen a ger who does hishtachavaya with pishut yodayim vraglayim in shemonah esreh, in fact his whole shemoneh esreh looks like an Arab prayer. Maybe there is such a shitah. I actually think he may have based it on a shitah that we can do pishut today, but I can’t recall his crazy rationale.
The point being that this is an extreme example of what happens when someone latches on to a mi’ut opinion that wasn’t mekubal by the majority of gedolim. It is a dangerous thing to do, it shows lack of emunah in the chachamim that came before the person and leads a person to be porush min hatzibbur.
On the other hand, the Rishonim, including the Rambam were (in comparison to us, not their predecessors) the mischadshim. They had the ability to write the Mishnah Torah and the Mordechai on their own cognizance. So the Rambam can have such a shitah.
But we, the collective jewish people, are not just talmidim of the Rambam. We are talmidim of the Rosh, the Ritvah, the Ramban, Rashi, etc. We are also talmidim of the Taz, the Vilna Gaon, the Ba’al Shem Tov, Rav Chaim Salanter, the Ben Ish Chai, Rav Dessler and myriads other gedolim who shaped our views and beliefs into what they are today. In essence, their teachings are the bedrock of all our hashkafos. The consensus among these gedolim is that there exists gilgul neshamos.
In my opinion, it is not the Rambam himself who carries Klal Yisroel, but all the gedolim together. And to throw out the majority of these gedolim in favor of one, requires strong shoulders, because you are not just taking the Rambam’s shitah, you are also throwing out the shitah of most gedolim from then and since then. If you want to do such a thing fine. But first reach the level of the Meiri or the Mechaber or the Besht.
To say that there is no gilgul neshamos is to throw out all the gedolim mekubalim and gedolim chassidus as well as many seforim that are based on that principle as being so much air. Who can say such a thing today?