Guys, before you flip out about precedent, do a little research. Insanity pleas are very rare. It varies slightly state to state, but on average, less than 1% of criminal defendants try the NGRI (not guilty by reason of insanity) plea. Around 70% of defendants withdraw their NGRI pleas once experts appointed by the state told the court that they were legally sane. Only 0.26% of NGRI pleas are successful. That's an incredibly small number, especially considering the number of people who go through the US legal system.

Drug use, as I said previously, does not qualify someone for an NGRI plea.

The definition of legal insanity is much narrower than the definition of mental illness. If you have the mental faculties to plan a crime, you don't meet the standard for legal insanity. The likelihood that someone could successfully fake insanity well enough to successfully plead insanity is very slim. Hannibal Lecter notwithstanding, most people simply aren't savvy enough to pull that off.

I'm not saying the system for NGRI pleas is flawless, but without fail, every time I see a discussion about it outside of legal circles, it's filled with unnecessary alarmism fueled by lack of accurate information.