In summary, a service has launched that allows dishonest users attempt to defraud merchants, and now Mike Hearn is proposing as a solution that we change the Bitcoin protocol to allow a majority of miners to vote on the blockchain to confiscate the newly-minted coins of any other miner.

If this proposal sounds problematic to you, that's because it is. As several other individuals in the thread pointed out, this fundamentally changes the nature of the Bitcoin network and adds a mechanism via which other changes the Bitcoin users do not want (blacklists) can be secretly added at any time in the future.

Why are fundamental changes to the Bitcoin protocol, with wide-ranging implications relevant to all Bitcoin users, being discussed in relatively obscure corners of the Internet?

It may be the case that email lists are where programmers feel most comfortable "talking shop", but it also remains the case that Bitcoin doesn't belong to them.

Bitcoin belongs to everyone who uses it. No amount of code contributions will ever give some set of "core developers" the right to impose their decisions on the rest of the network. In fact, the degree to which they recognize that fact is the exact degree to which they will remain relevant to the future. Bitcoin users have a choice of software implementations these days, and implementations which attempt to rule the network instead of serve it will be dropped.

Individuals wishing to propose existential changes to the network should have that discussion in the public sphere, where the users are, so that those users have the best information possible regarding which implementations they should trust.

Core developers are not philosopher-kings who rule the network by imposing their judgement on the hoi polli, and they shouldn't act like it. (Note that this is not the first time Mike Hearn has floated proposals he knew Bitcoin users wouldn't like as trial balloons in relative obscurity). Once there is consensus among the community, or at least after they are aware of the proposal, then the development mailing list is an appropriate place to discuss how to implement it.