Immortality would be beneficial for us for following reasons:
1. People suffer from shortsightedness. If you would live indefinitely, you would be more concerned about environment and more interested in investing millenial projects such as interstellar travel which is gonna be neccesary at some point.
2. It makes us more careful. We would think one more time, before we engage in pointless wars if we had more to lose. Common mentality with people is "well, i die anyway so lets make it count" when it comes to war for an example.
3. It makes us appreciate others more, for the same reason as above. I think lifes value increases indefinitely if life expectancy is indefinite.