I can't give blood because I have Hemochromatosis. Even though I've to get one unit of blood taken every 2 weeks by my GP, I cannot donate blood. The blood that gets taken from me is just thrown away, regardless of there being nothing wrong with it. Its a genetic disease that causes your blood to be overloaded with iron, which means the blood would be ideal for people who suffer with iron difficiency enemia. It does not effect the safety of the blood in any way.
In places like australia they accept donations from people with this disease, but over here they do not. I know that Hemochromatosis is very common among the Irish, so there must be plenty more people out there who have this disease, who are getting blood taken from them and thrown away, when it could be going to blood banks.
I think a petition is in order!