Where does it say that the Rambam went on the Temple Mount? And if he did so, why are some rabbis against going up?
It’s cited in the Mossad HaRav Kook edition of Igrot HaRambam, p. 79: “On Yom Shlishi, 4th of Cheshvan in the year 4926 since creation, we left Acco to go up to Y’rushalayim, under danger. And I entered the great and awesome Bayit (literally: the House, the place where the Beit HaMikdash stood) and I prayed there, on Yom Chamishi (Thurs.), the 6th of Cheshvan.” The main opposition today is because most who go up to Har HaBayit won’t do the necessary preparations of combing, cleaning and cuttings nail and hair, going to the mikveh without any chatzitza (men aren’t used to this), changing to house-slippers, etc. In addition, they may accidentally go into the area where tmei’ei mett (those who were in contact with the dead, which is just about all of us) aren’t allowed (and where mikveh doesn’t help). On the other hand, there are many religious who do go up and are very careful regarding the above, and they feel that if we don’t go, it’s like we’re leaving the Temple Mount in the hands of gentiles. They also feel that those non-observant who go up improperly and with shoes, will do so anyway, and it’s not because they misunderstand those religious who do go up.