What is the purpose of life ?

The question assumes there is a purpose. I don't think that's a safe assumption :)

It all depends on what you define as life. Your question, while purely academic, is a perfect of example of the human NEED for meaning. We make our own meanings, we mold our life into having purpose, through friends, family, dreams and goals. Sorry four sounding so "after-school-specialy", but I really do think that.

Life, as biological process, has no clear purpose other than to keep the process itself going for as long as possible, and as efficiently as possible.

I really don't think I've answered you quite sufficiently. If your question is serious, would you provide more input as to what exactly you mean? 

Again, from a purely academic point of view, you simply weigh the good and the bad. If you have Cancer, and that fact outweighs the benefits of living (family, friends, movies and booze), then you're right: you shouldn't struggle.

But then there's the personal point of view, the social taboo this represents, the people you'd hurt via whatever action you choose to end your life. People have a hard time letting others go. And even if he's ready to go, wants to go, people still can't accept it.

What you're doing now, reading this answer, typing a new question, hurting, rejoicing, whatever - all that is life. On the the other hand, we have death, where no one is waiting for you , where there is no serenity, no peace. Just a whole lot of Not. Choose life because it beats the alternative. :)