Didn't Spock refuse to donate his blood to save a dying man?
And wasn't he berated by everyone including his own mother despite it being a fairly risky operation to himself.
He was, but it wasn't his personal values preventing him from doing so. But his duty to the ship when Kirk was injured.
If it had just been going to sickbay to donate a couple pints, he would've done it without hesitation. The drug needed to amp up his blood production would've taken away his ability to do his duty to protect the ship and Federation delegates.