This is developing into quite an interesting and fun set of debating points. I'll play along for a while:
Of course I would, and this is a complete non-sequitur of a question, confusing as it does two totally unrelated and non-reciprocal ethical questions.
Even if you create the stipulation that one should only feel morally sound about accepting a transfusion if contributing something in return (which, incidentally, is a stipulation I do not agree with), your equalling the act of donation with the act of receiving a transfusion is still completely flawed. I can explain why by highlighting its flaw:
The only way to fix your argument would be to insist on an extra restriction that one can only benefit from a concept if you directly contribute to it in exactly the same way. It seems bizarre to suggest this, since our entire way of life is built upon transactions mediated via an arbitrary third party (fiat money).
If you accept the concept of money, you automatically accept that like does not need to given in order to receive like. You can trade goods according to an arbitrary scale. Similarly moral authority is interchangeable and can be traded similarly. So if one were to contribute to "the greater good" in another way other than donation of blood, you would still gain the moral authority to receive blood, even if you did not donate blood yourself.
Of course, since there is no external arbiter of moral worth who can operate on a fine enough scale to judge relative worth in this way, a "fair market" can't actually operate in practice, and the only deteriminant becomes one's own conscience. ie. back to square one!
Nice? Sure. It would also be nice if the government didn't take so much money from me in the first place, if turning on the kitchen tap resulted in a cascade of Chateau d'Yquem, and if Anne Hathaway was busy whispering sweet nothings in my ear.
None of these nice things are likely to happen however and at least my choices have the added benefit of making my day better, which going to donate blood or whatever most certainly would not.
This comes back to the "where do you draw the line" issue I raised earlier in another post. To me, it's not even the physical pain that's at stake (as you say, that is largely trivial), but rather the fact I have less than zero motivation to go donate to a stranger at all. Why should I?
Others will doubtless say I am being selfish on this issue. I would agree with them. I would also say that I see no moral problem with this given that there are many other areas where I consider myself most unselfish (referring back to the argument about arbitrary moral trading above).
Again, we all choose where we exercise our selfishness and where we are generous, as none of us are as saintly as we sometimes like to pretend we are. I am selfish by not donating blood; every person on this board will be selfish in a different way. We operate in a morality largely run according to rules we ourselves have created. I don't see anything wrong with that. The ultimate determinant of these issues as I see it is whether we are comfortable in our own consciences, not in someone else's.
Most of us use this sort of "fuzzy moral calculus" all the time without realising. But that doesn't mean it's not happening under the surface. I personally feel that understanding and accepting our essential moral fuzziness is actually enlightening for mankind in the long term.
Would you take another person's blood or marrow if you were the one injured or sick?
Of course I would, and this is a complete non-sequitur of a question, confusing as it does two totally unrelated and non-reciprocal ethical questions.
Even if you create the stipulation that one should only feel morally sound about accepting a transfusion if contributing something in return (which, incidentally, is a stipulation I do not agree with), your equalling the act of donation with the act of receiving a transfusion is still completely flawed. I can explain why by highlighting its flaw:
The only way to fix your argument would be to insist on an extra restriction that one can only benefit from a concept if you directly contribute to it in exactly the same way. It seems bizarre to suggest this, since our entire way of life is built upon transactions mediated via an arbitrary third party (fiat money).
If you accept the concept of money, you automatically accept that like does not need to given in order to receive like. You can trade goods according to an arbitrary scale. Similarly moral authority is interchangeable and can be traded similarly. So if one were to contribute to "the greater good" in another way other than donation of blood, you would still gain the moral authority to receive blood, even if you did not donate blood yourself.
Of course, since there is no external arbiter of moral worth who can operate on a fine enough scale to judge relative worth in this way, a "fair market" can't actually operate in practice, and the only deteriminant becomes one's own conscience. ie. back to square one!
Now if you have to take time off work, I think it would be nice if you could be compensated for that by the government so that you aren't out of pocket.
Nice? Sure. It would also be nice if the government didn't take so much money from me in the first place, if turning on the kitchen tap resulted in a cascade of Chateau d'Yquem, and if Anne Hathaway was busy whispering sweet nothings in my ear.

None of these nice things are likely to happen however and at least my choices have the added benefit of making my day better, which going to donate blood or whatever most certainly would not.
So really all that you should suffer is a little physical pain. To me that seems to be a very small price to pay to save a life.
This comes back to the "where do you draw the line" issue I raised earlier in another post. To me, it's not even the physical pain that's at stake (as you say, that is largely trivial), but rather the fact I have less than zero motivation to go donate to a stranger at all. Why should I?
Others will doubtless say I am being selfish on this issue. I would agree with them. I would also say that I see no moral problem with this given that there are many other areas where I consider myself most unselfish (referring back to the argument about arbitrary moral trading above).
Again, we all choose where we exercise our selfishness and where we are generous, as none of us are as saintly as we sometimes like to pretend we are. I am selfish by not donating blood; every person on this board will be selfish in a different way. We operate in a morality largely run according to rules we ourselves have created. I don't see anything wrong with that. The ultimate determinant of these issues as I see it is whether we are comfortable in our own consciences, not in someone else's.
Most of us use this sort of "fuzzy moral calculus" all the time without realising. But that doesn't mean it's not happening under the surface. I personally feel that understanding and accepting our essential moral fuzziness is actually enlightening for mankind in the long term.