Living forever isn't all it's cracked up to be. I've had the conversation with a couple of people (so my results are purely anecdotal and should be interpreted as such), and it's my experience that people don't really think about just how long *forever* is. Imagine living for just 150 years. Pretty much everyone you've known is going to be dead. You'll have the opportunity to meet new people, sure, but if you know that all the people you'll ever meet will be lost to you at some point (when they die), what's the incentive to live forever?
Even assuming that you could do some good in the world, which isn't given at all, eventually the Sun will expand and all life on Earth will die. Then the planet might get struck by some huge meteor and you'd be floating out in the vastness of space until *time itself* came to an end. Doesn't sound that great to me.
I'd much rather take the limited amount of time that I have to try to improve my life and the lives of those people that I love. I know that every atom in my body was once a part of a star, and I like the idea that eventually I'll be returned to that state. Just makes everyday life much more enjoyable, and meaningful, to embrace your finitude.