I asked this same thing to my father, he replied that when a person uses blood; it IS a sign of spiritual weakness, in his opinion. But up to god to judge him. HE then recalled a sister that took blood and when asked by fellow members of the collective; she was telling them openly, with no shame, hey why not? She was happy to be alive. But then the elders counseled her not to say ANYTHING about her medical treatment for fearing she may stumble those in the collective... The verdict? You can now use it, but DON'T ASK, DON'T TELL. That seems to be the unwritten rule, the one that's unknown by the rank and file.
I know I was stunned too when I heard it from his face.
jojochan.