Life would be so sad if we had a purpose. We'd be like tools in a toolbox, waiting for accomplish our duty and then when we would be no longer useful, we'd only have to dissappear. Biologically, yes, our 'purpose' is to reproduce... but we're rational animals. We have more potential than that.
Purpose is what we decide, the goals we set and our preferences towards the future. Some wish to help mankind, others are 'antagonists'... yet, it's that conflict of interests what makes life so interesting. The way is the true goal. Finding our purpose... maybe that's our real purpose.