If you can donate a sperm, How could that be different from donating an egg?
Donating a kidney is rather different, as you can reasonably expect to regenerate a sperm or egg, and if you give one away or just flush it, this will not change the quality of life in any way, at least if it is anonymous., but life with one kidney could be a major problem.
I don't see where the government should get involved with trafficking in eggs and sperm.
There are good reasons for requiring some sort of careful supervision regarding the sale of kidneys and other non regenerating organs.
I am willing to sell excess hair and fingernail clippings, by the way. Not that I have actually been saving for such a contingency arising, but I could if there was a market available...