Agreed. I would not propose a blood boycott, and I would likewise endorse giving blood, with no teeth-gnashing involved. I would even (reluctantly) endorse the current FDA standards if doing so could be expected to increase the amount of blood donated in a non-trivial way. What I would not do is endorse the current FDA standards as rational, especially in the context of a discussion about doing rational things.

If my objective is to promote rationality (and achieving ends I value ethically is also a consideration), I would want to instead endorse some activity or organization that is approximately as fuzzy but lacks current controversy over its willingness to adhere to scientific standards, noting that said controversy is still bad (given this particular objective) regardless of whether it is warranted. If I am concerned about the public perception and adoption of rationality, I should maximize for that value.

That the controversy centers around a standard that is both sub-optimal and needlessly discriminatory is merely gravy.