You need cryptographic identities for automated boycotts. Boycotts aren't very effective today because they're hard to organize, and some vendors have relative monopolies. I think Ethereum enables both effective boycott coordination and monopoly elimination.
Also, these sanctions apply to both sellers and buyers. I think economic isolation will be an effective deterrent to undesirable behavior. It's basically prison, just without force.
Imminent harm may be a slippery slope, but it's really all up to the individuals who support the enforcers. If someone detains someone who shouldn't have been detained, stop funding their activities and sanction them. Fund a different enforcement organization instead.
