I concede your points, but people who don't want to be photographed at an event which of its very nature is much photographed, just need to be aware of that and stay out of range of the viewfinder. That is not a Herculean task.
The goal of Wikimania is not to produce pictures of Wikimania, but to attend to conferences and share experiences, build new projects with others, etc.
And Even with the OK photo lanyard, it does not mean people like to be photographed in ridiculous situation or when eating food, etc.
So this is not an herculean task, but it's up to the photographer to get it right, not the other way around.