To use a comparison, consider a man who is told by the doctor that he must abstain from alcohol. Would he be obedient if he quit drinking alcohol but had it put directly into his veins?
And of course everyone knows how to refute this one, right?
It's comparing apples and oranges. Alcohol consumed orally or injected into the veins is processed similarly within the body, while there is a huge difference with regard to blood.
Blood that is eaten is attacked by enzymes, broken down, digested, and converted into energy. Blood that is transfused becomes part of the body - it is in effect an organ transplant.
A more accurate comparison would be, "Consider a man who is told by a doctor that he is starving to death. Would he survive if he refused to eat but consented to a liver transplant?"