This reminds me of "The Copenhagen Interpretation of Ethics": http://web.archive.org/web/20160806191858/https://blog.jaibo... Our culture has a very strange belief that you shouldn't benefit from the less fortunate. Even if you benefit them too. People that have never donated a dollar to charity in their lives, will come out of the woodwork and complain about "exploitation".
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.