If you're deceased, what sort of labor are you doing exactly?
To me, your argument seems to fall more along the lines of your body and organs being property that can be inherited by your family in the same was as cash, real estate, etc. Which is an interesting idea.
But ultimately it's called "donation" for a reason. If you donate to, say UNICEF or Red Cross, you're also the only one in the chain who doesn't get paid.