Because testing all donated blood is prohibitively expensive, and not all testing is completely accurate or able to detect recent infection. People are barred from donating blood for all manner of possible exposure to disease, for instance if you’ve traveled to certain countries. It’s not just gays.
If someone who is gay wants to donate blood all that badly, I’d be willing to consider it if they certify that they’re tested for a full STD panel monthly and are held legally liable for damages if any recipient(s) are infected with HIV or Hepatitis C as a result of their donating blood.
http://www.freerepublic.com/focus/news/3440457/posts?page=35#35
See that post of mine in this thread. It discusses how the FDA already settled all this. They issued a long report last year that went through all the studies they’ve done on the issue and thoroughly discussed all the options. It left no stone unturned. And they concluded the ban was necessary.
Yet virtually every mainstream media outlet is publishing a “lift the ban” story and completely ignoring the FDA report that is publicly available online.
That report is a GREAT, definitive resource, with answers to every question on the issue. I posted excerpts from it here:
http://www.freerepublic.com/focus/f-news/3440453/posts