"People that have never donated a dollar to charity in their lives" is a particularly American, or let's say anglophone, way to approach social justice.

Charities are based on good will, but "the less fortunate" do not need "good will": they need social rights. https://en.wikipedia.org/wiki/Social_rights

If you don't see "exploitation" when people need and they are willing to sell their blood, I have no idea what you mean by exploitation.