After a person has accumulated enough issues unresolved, and to which his opinion or want makes little or no difference, it seems the only way to find peace is to give up. To say of all self-interests: it doesn't matter. Then he is in harmony with the universe, because to the universe it doesn't matter.
One reason a single person should volunteer is to matter. I am not on a mission to make a difference; I am not the confident crusader. I just want to matter to someone besides myself. I know there are many who feel as I do. There are those who have become so reserved as to withdraw from the world, perhaps even with a wish that someone would ask them to come back. But the world goes on, and if you withdraw from it, you won't matter to it. While it is very difficult to step out when you have been pushed back so many times, it is up to you to interrupt the world.
While you may even want to resort to violence just to get someone's attention, the better way to interrupt is with kindness. Can you care about someone you don't know, as volunteer opportunities afford all the time? Don't you wish someone who doesn't know you yet would care? The world may not notice an act of kindness because, frankly, it may not even recognize it, but one individual might.