Animal rights activists had pushed for the ban which could prevent kosher and halal ritual slaughter which requires livestock to be conscious when their throats are slit.
I know animals must be healthy, but being stunned isn't a disease, so why must they be conscious?
Most of the comments and answers explain why pre-stunning is not a good idea (both because if under-done it could be less humane, and because if over-done it could have caused an undetectable fatal injury, which would make the meat non-kosher).
These explanations are useful and informative, and certainly I have no disagreement with any of them, but that is not what I'm asking.
The popularly published information isn't that the animal shouldn't be stunned, but that it "must be conscious".
I am asking where this requirement for consciousness phrase comes from.