Should we practice pro bono work?

We are living in a very pragmatic world and the capitalism system taught us that everything has a price and almost nothing is for free. Fortunately, not all of us are so addicted to this idea, there are people that have as the main scope in life to help other fellows. The huge majority of us are situated in between positions, not very avaricious to avoid any help but also not so altruist to give everything we have. The web designers are normal people (maybe too dependent on Internet) and respect the same pattern, from time to time they work on project expecting no payment, the so called pro bono work.