Dear Pa Grape,
I don't want to support sperm donation, but I think your argument here is flawed. There are ligitimate reasons why sperm must be collected; it's the first thing they test when a woman can't get pregnant. So the issue isn't the act itself, but the reasons behind the act.
I believe he was mainly referring to donation for the case of fertilization.
And for money.
If sperm are collected for diagnosis of a potentially infertile married couple, then... [How do I put this?] the required activity could be as a couple, which would remove any concern about the appropriateness of self-stimulation. [That's pretty good, I think.]