Recently I was trying to talk someone out of suicidal thought and he replied along the lines of "no one asked for my permission when they brought me to this world so it's my right to leave without their permission". Thank god he didn't actually do it but does that argument carry any weight? Would a philosopher be persuaded? If so surely anyone could freely commit suicide?

There's a fine book by Jennifer Hecht called "Stay," that outlines the many different positions philosophers have taken on the topic. It's a fascinating read. For myself, I don't wholly agree with your friend's claim. I do partially agree in that I think individual autonomy, including autonomy in the decision to end one's own life, should be valued a great deal and overridden only for very good reasons. There are, however, some very good reasons to override the choice of suicide in many circumstances (not all). Here are two I find compelling: (1) obligations to our future selves and (2) the effects of our lives upon others. The basic idea with (1) is that your current self is not the only iteration of you that will exist. In the future, things might be very different, many people miserable today are happy and virtuous later in life. Moreover, our later selves are dependent upon the survival of our current selves. That dependency matters--which brings me to (2). With (2) the important bit is to realize...