Avirah, first of all, Rav Soloveichik earned a doctorate in philosophy. rav Kirsch himself studied philosophy as did Rav Kook, his son rav Tzvi Yehuda and one of his main talmidim, the Rav haNazir (Rav David haCohen). Rabbi Jonathan Sacks also studied it. He as well as many other rabbis, both in America and Israel quote non-Jewish and secular Jewish writers. Of course, someone who wants to study it should have a rav. This also depends on the branch of philosophy (logic, which is very mathematical in nature, is considered a branch of philosophy) and why one is studying it. Some just want to learn how to formulate arguments. In fact, when someone asked Bertrand Russell why he did not live according to his theories he replied that he was also a mathematician yet no one expected him to be a triangle.
As for Rav Meiselman’s book, he is attempting to show that Chazal were not wrong about science. I personally have my doubts as to whether or not they meant their statements literally (the Ben Ish Hai seems to take them as metaphors and Rambam says that all the aggadatot were metaphors). However, it is clear that they interacted with non-Jews and even admitted when they were right (Pesachim 94b). Shmuel went to a debating club called Bei Avidan (Shabbat 116b) and had a number of conversations with a non-Jewish sage named Ablett.