Philosophy should absolutely be compulsory. The very nature of the world itself and all we know runs off of some form of philosophy and people are seen daily professing beliefs in concepts they don't understand because they've never even bothered to study philosophy, logic, or other core concepts relative to thinking.
Philosophy is the literal groundwork for all theories, scientific or otherwise, and with no understanding of it the very mechanics of all theories, scientific or otherwise, are lost to the individual in entirety.
Philosophy undermines all knowledge itself, that being said, philosophy ties in humanities, business, maths and science. It would be highly advantageous for a student to learn fundamentals of knowledge so they can assimilate their studies to a greater extent. It adores not need to take up much time on the curricular, it just needs to be present. Philosophy also gives us humanities greatest tool, logic. The logical deduction provided by philosophical thinking can gelp in he mathematical and science studies not to mention that philosophy can also add depth to a students understanding of the world around us. As for the lack of interest argument, I personally believe this argument is flawed due to how our modern education system works. Students don't get to choose what they study because they like it ( that occurs in senior years ) they study it because someone in the government said they should learn it. I personally hate maths but I still have to learn it. Also, the philosophy taught does not need to be incredibly complex. It would obviously be toned down for the students year level.
Philosophy should be pursued on owns accord. To truly enjoy the subject one has to develop an interest in pursuing knowledge and have the ability to analytically engage in debates. Furthermore, philosophy involves various technical writings and can be intimidating to engage is one does not have the sufficient expertise in language to comprehend them. I am not claiming that students below Year 11 will not be able to totally understand the concepts. Some will, and some won't. Philosophy, in my opinion, should be made available to students after they have develop a concrete foundation of knowledge varying from different spheres, so that they can truly understand the implications behind certain field of thoughts and the big questions that we've yet to solve.