i would say that the purpose of life is to live it and enjoy it. To be happy, but not too much so - not being too happy or sad can also bring happiness. One must balance one's emotions in order to have a good, long lived life.
There is a certain type of happiness that comes from living one's life for the betterment of others. This is not to say that this can't be achieved by selfish means - but many times it will be. Either way, having lived an altruistic life tends to make people happy in their old age.
I think that happiness is the most important thing in life. It can be the difference between a good or bad life, and I believe that if one lives for others as well as for themselves, they will find their true purpose.
In my opinion, it is the duty of all members of society to maximize their happiness. A happy person will help others be happy - and a sad person can spread depression. Both these things are undesirable.
I think that living a life in which you live for others is the best way to find your true purpose. If you want to be happy, then make other people happy.
It's good to be happy - but you must live for others, not just yourself. It is the right thing to do.