Razorblade, you and I have something in common. I'm "out" of the borg since '82, but the affects of it lingered on with me until three years ago, when I finally rid myself of all that deeply imbedded dogma and falsehood. Like you, I began to open my eyes and my heart to the real world and living in it.
Donating blood is very private the way it's handled. They ask lots of necessary questions, which are very personal, but totally private. You answer them the best you can, as truthfully as you can. Even later, you can change your mind about donating. There is no pressure at all. And, your blood will be checked for many things and you will be notified if something shows up, so you can get checked by a doctor. Believe me, the blood people receive in transfusions goes through quite a process.
You don't have to be physically fit, and you can have diabetes, high blood pressure, high cholesterol, etc., and it does not affect one's ability to donate.