What's wrong with dying? We all do it sooner or later as individuals. Why should the race last forever?
Because we may be the only chance for life on earth to spread to other planets,
If we botch it this time, life may not have enough time to evolve another space faring civilisation. Think about it. Though doing nothing we may seal the fate for all of life.
We are part of a much larger ecosystem, without which we cannot survive. If we travel to the stars, so does life - which will continue to evolve.
If there is some great project humanity should try to tackle, it would be this.