I personally think Philosophy should be a class in high school for upper classmen, regardless of it being optional or not.
Philosophy offers the ability to freely think critically about the biggest questions in life most people are afraid to answer. Reading the great works of Western and Eastern philosophers would help students find peace and happiness in oneself and with the world around them, and fix the flaws to lead to the most fulfilling life at an important stage in the cycle of life. But in the end, you decide what's best for you, because you know yourself better than anyone else ever could.
Philosophy isn't very useful. Secondary education is all about continuing to build a solid foundation of conceptual and practical skills to be applied in a entry-level career, or to prepare for tertiary education. Simply put, at the level of secondary education, most people are not developed enough and/or lack a basic understanding of rationalism to make it of any use.
You're pretty much asking someone to talk about physics without having an understanding of algebra.