I moved the big meta-level comment thread from "Yes Requires the Possibility of No" over to here, since it seemed mostly unrelated to that top-level post. This not being on frontpage also makes it easier for people to just directly discuss the moderation and meta-level norms.
I see no reason why you are not allowed to discuss a specific example when someone talks abstractly when you consider this example to be important.
If you think the principle advocated in a post like Where to Draw the Boundaries? gets case X very wrong, it would be illuminating to write out why you think the principle that's advocated gets case X wrong and how that shows that the abstract principle is flawed.
It's harder to defend as that means you actually have to articulate a coherent concept of the concept of identity and argue why that concept is better then Where to Draw the Boundaries? but it's very far removed from saying that you are not allowed to defend yourself.
As far as the norms of double crux goes, when there's an object level disagreement and the crux seems to be on a higher abstract layer, the standard way to proceed would be to actually discuss the higher layer.