Vegan advocacy groups should consider regularly donating blood as representatives of their groups. At my local blood donor centre (in Australia) there is a poster in the waiting area where companies/orgs are listed in order of contributions. Having your group up there will likely help to dispel:

• perceptions of vegans as dissident outgroup members (i.e. they can have more traditional and "common sense" values, norms and cares as well).
• myths regarding poor health.
• (getting even more speculative and not even sure this is a thing) myths that their moral position is based on being overly squeamish rather than rationality.

On the second point, another reason is that myths regarding poor health are not entirely unfounded, and vegans are more likely to have low haemoglobin which is tested prior to donation. Once for me, it was slightly low and I was asked to get another official test before donating again (it was fine in the subsequent test, probably in part to me deliberately upping iron intake including a daily vitamin). They test for other things as well - infectious diseases as standard before transfusion, but I believe it could be tested for anything if the blood ends up being used for that purpose (in which case, you would be informed if there is anything to be concerned about, however I suspect this scenario playing out is quite rare)