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.
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I'd say keep it as an elective, but only for the reason that it takes [i]quality[/i] instruction to do right. Putting philosophy in the hands of an incompetent teacher would make the course just about useless.