Should organ donors be praised as heroes? Mickey Mantle said so. Luckily, I didn't grow up in New York in the '50s, so I can disregard Mick. Their donations can save over a dozen people and I am not questioning that. I do, however, want to make a few points.
Cadaver donors - I am not talking about live kidney donors or partial-liver donors - do not make a decision at the time of death to give anything. They made a choice earlier - or their family did - and sometimes the situation does come when, while they are are at least unconscious and at most dead according to some authorities, their organs are harvested. There is no "cost" to them to donate.
People who donate blood regularly help many people - as many as three people with one donation. Their donation is voluntary. They have to take time out to donate. They are inconvenienced - albeit minimally - but they consistently and voluntarily give up time and "a pound of flesh" (reviis dam is metamei lemais like basar, see Sanhedrin 4).
And to register on the international bone marrow registry can save lives even if you are never asked to donate stem cells or bone marrow (see this post). Kind of sounds like the spiel they always give you when you show up for jury duty.
My Rebbi zt"l discussed some of the classic questions about Akeidas Yitzchak. Why was it considered a test of Avraham and not of Yitzchak? If Hashem hates human sacrifice, what was His goal in asking Avraham to offer his som? Why doesn't the Torah say that Yitzchak returned with Avraham after the Akeida?
Please read his entire discussion in The Warmth and the Light. Briefly, he discussed dying for a cause and living for a cause. Some people are willing to die for a cause, but they are not willing to do little things every day for the same cause. Avraham did not let Yitzchak go to Yeshivas Shem v'Eiver until after the Akeida because he loved Yitzchak so much, he didn't want to be separated from him before the Akeida. Explaining the Ramban, my rebbi said that once Avraham saw he was willing to sacrifice Yitzchak because G-d said so, he realized he could make the smaller, everyday sacrifices regarding Yitzchak.
UPDATE: See here - The Hoffer wrote about this same piece this week. He brings more depth than I did.
Some people can set a big goal, to run a marathon. They take big chunks of time over half a year to train. Is it actually healthier for them to do this or to exercise on a regular basis, with probably shorter training sessions, but keep it up for the long term?
So which is greater - the organ donor or the regular blood donor?
I don't know.