I hope that the people who want to stop police from using this as a defense are also willing to stop murderers from using it when they are begging to not get life without parole.
What are you even talking about?
The asymmetry obviously being that arguing you shouldn't be responsible for what happens when the pharmacy runs out of your anti-psychotic medication is very different then arguing that you shouldn't be responsible for beating down some distressed mentally ill civilian when the pharmacy runs out of their anti-psychotic medication.