Brasas: Try to see it as a defense mechanism. Much as they like to believe themselves sophisticated, most of the folks using the block list are rather fragile greenhouse flowers. Given the emotional outbursts when they are confronted by different opinions, and since isolating them is ethically wrong, I can't say their trying to self isolate is inherently problematic. Probably helps them function. The slander of course, is a separate matter.
On a personal level, I don't care if a person chooses to use a block list. Its their personal decision to do so, and they're the ones who have to deal with the consequences. And for most people, that's even fine, we don't talk to every person in the world and we're not likely to get along with everyone. Personally I don't like the idea of using someone else's definitions when they've been so loosely defined, but eh, I'm me, not them. If it makes them feel comfortable, and it's the choice they've made with the power they have, then fuck it, who am I to judge?
As far as the IGDA...that's another bag of worms, and I'm FAR less forgiving for an entire organization. They should have vetted the damn thing and known how easy it would be to have false positives on it. They should have someone who checks the damn list so that it doesn't blatantly have developers on it, that it doesn't have one of their own chairpeople on the godforsaken thing. I can't comment on the code itself, so sadly someone else will, but I can judge on the basis of the list itself, based on who follows certain people that have not been accused of harassment, but instead have been outspoken Pro-GGers, it feels more like it's ideology driven and that's pretty dangerous, especially since anyone can grab it without realizing that it's being misrepresented as a more positive thing then it really is. It feels like there has been no effort into vetting the list or being honest with people.