My answer to this is hella simple. We're here, and a reason doesn't matter. The fact is that since we're here, and there is nothing we can do to change it, we can do whatever we want. The only rules we are bound by are our personal morals. To each individual following rules, laws, and other people's opinions is optional. In this way, the choices of how to live your life are infinite. I personally, however, choose to live in a way that makes me happy. This means doing anything that I can enjoy. Right now, that means playing video games, working out, fucking bitches, and getting good grades in school so that I can do all of this on a larger scale. However, I'm not saying that this is the only way to achieve happiness. If I was so inclined, I wouldn't be object to breaking rules or laws to pursue my happiness. For if you think about my philosophy of achieving happiness, individuals are not limited in their pursuits, nor guided.
So at the end of the day, the reason why we are here doesn't matter. Take it as it is, and work with what we are given. There is no guarantee that tomorrow will come, and no guarantee that when we are dead, the world will go on. Do what makes you happy, and if you want to, do for others what will make them happy as well.