I actually have reasons to be against organ donation, and I will give my reasons, and they are the amount of drugs that the person needs so that the body does not reject the foreign object in their body.
A good friend of mine, when his dad was still alive had a kidney transplant, (cant recall, think it was both kidneys), there was a lot of drugs needed. Now at some point, from what I understand, when those kidneys gave out, never went for another, and just stuck with dialysis.
In order for a body to accept a organ from someone else, one needs those Immunosuppressant Drugs. The fact that people need such powerful drugs in their body to accept a foreign organ tells me a lot.
This is my opinion, and everyone is entitled to their own opinion on this, but I see organ donation as a means for the drug companies to make money of people's suffering.