Would it be asking too much that you actually read the Butler text to which you're responding? She's replying to exactly the sort of argument you're making here.
> I brought up gas chambers not because sex is so grave a matter but
> because I suspect that people who hold the Butler position lack the
> courage of their philosophical convictions. If they really think it's
> unfounded to refer to anything extra-discursive and should limit
> ourselves to references to discursive constructions of things, does that
> view extend to those aspects of (okay, I'll say it) reality that they
> think are really important? If not, why not?
Wait, you think that Butler only holds the position she does about sex because she doesn't think sex is important? That would be an odd thing in a feminist and queer activist.
One could apply Butler's questions about the discursive constitution of materiality to the holocaust; people have probably done so, although I'm not aware of the particular works. Saidiya Hartman's _Scenes of Subjection_ uses some of Butler's ideas in relation to slavery in the US; but it would be incredibly stupid to read her work as denying the existence of slavery, just as it's stupid to read Butler as denying the existence of biology.