If you are going to have sex with someone, you know your risks and decide to take them.
Getting a unit of blood is something you get in an emergency, and you often aren't even awake when you are given the blood.
But you will never get my blood. Because I lived in Europe in some year late in the 80s when England had a mad cow scare (I wasn’t in England and I never ate beef from England), I am banned for life from donating blood in the USA. But any gay man who checks the box that he hasn’t had sex in a year can give.