Disassociation versus disfellowshipping is an interesting discussion for several reasons. Morally, one thing matters: both are procedures put in place by the WTS to impose shunning. That is the bottom line.
1. Both are mechanisms of the WTS.
2. Both operate under rules established by the WTS.
3. Both are used to impose shunning.
4. In terms of blood use, both require the judgment of a committee of WTS appointed elders. (This is not a “judicial” committee. “Judicial” committees are those used in procedures that might lead to “disfellowshipping”)
Everything else is smoke and mirrors designed to fuel legal arguments and accommodate social and/or political perceptions. Discussions here and elsewhere inevitably swirl around two topics. 1) Legal arguments that one poses versus the other, and 2) how to cut through WTS assertions about the two so society can see both for what they are, the same thing: procedures to effect shunning, shunning that is instigated and imposed by the WTS through its appointees.
On the legal front, disassociation is designed to add a dynamic (or frustration) to the question of liability arising from defamation. Slander or not, people’s character can be assassinated by certain circumstances, and that brings civil liability in most developed lands, usually irrespective or laws designed to protect freedoms of worship. When assertions arise of character assassination, disassociation is designed to place an additional weight of evidence onto the accuser. If a judge (or jury) buys this scheme—which sometimes is legitimate—then the accused is forced to show evidence that his or her actions would not have inevitably resulted in the same defamation. That is the additional weight of evidence. In the case of accepting a transfusion of blood, if the only persons knowing of it are legally bound medical professionals and congregational elders, then the idea of inevitability disappears in practical terms. This is the legal Achilles heal, but it only refutes the one aspect of inevitability, it does not win the suit. To win the suit a person must evidence that character assassination is a fact and that the WTS or its appointees are responsible.
To illustrate, cases of inevitability are pretty straightforward in cases of JWs joining an army. This is an action that would inevitably become known regardless of any congregational announcement or leak in confidentiality. These sorts of actions are perfect candidates for the legal argument of inevitability in cases of defamation. Adding to this is the fact that when a JW joins an army there is no judgment related to repentance; disassociation is automatic. This is not the case when a JW accepts a medical transfusion of blood. This act could be done under the authority of medical confidentiality. Leaks must then come as a result of confession, leaks in medical confidentiality, or else congregational snoops. If defamation arises from breaching medical confidentiality or congregational snoops, then those responsible for enacting the procedure of “disassociation” become legally liable for that defamation. If the legal argument of inevitability disappears then the playing field is leveled back to what it would be for disfellowshipping.
In the end, the problem boils down to this: assuming congregational elders act as told, in most developed lands the gain is no more than getting rid of a false legal argument called here inevitability. Because laws protecting religion’s freedoms are usually strong, legal suits over shunning are notoriously hard to prevail in. As long as a religion’s practices are reasonably well known then, unless a principal in the affair acts outside established norms, they can pretty much do as they please. The WTS’ norms on shunning are reasonably well known to JWs.
I will leave the aspect of social/political perception for someone else’s elaboration; a perception the WTS hopes will enhance its public relations.
I believe other posters have done a good job addressing this subject. I thought it deserved its own thread.