I don’t know that I have an answer for you, but let’s start thinking our way through this…
First off, the assertion that “the Blood of Christ kills you” is absurd on its very face. It’s the
arsenic that kills, not the consecrated wine.
Second, there’s the question of how the arsenic is distributed through the wine. Does it become part of the wine itself, or is it now a mixture (homogenous or otherwise) of wine
and arsenic? Does the doping of the wine with arsenic change the nature of the matter?
Third, there’s a difference between adding something to the ingredients that become wine and adding something to the final product itself. Likewise, you’re asserting that you’re adding sugar or yeast to the
flour, not the finished product of Eucharistic
bread, right? Therefore, the bread is invalid matter from its very origins as ‘bread’.
Finally, there’s the question of intent, it seems. If someone caused the matter to be invalid, then the Eucharist, properly speaking, would not be confected. Yet, we would assert that God would supply the graces that
would have been gained through reception of the Eucharist, if it had been present. (I’m not asserting
ecclesia supplet, by the way.

)
Still knocking this one about, in my mind, but those are at least my initial thoughts…