Does mental illness affect whether or not someone is given the death penalty? The simple answer is, it depends. It depends on where you live, what your ethnicity is, the judge and their personal beliefs and opinions. The court has yet to hold that a person has a constitutional right not to be executed while insane, notwithstanding the multiple cases that have leaned in the direction that there should be. 
One of the most common arguments in this debate is that it is "simply... unnecessary to put the insane prisoner to death." This position states that an insane person’s life is more important than the person or persons life that was affected. Therefore disregaurding the 14th amendement which guarantees “equal protection under the laws”.​​​​​​​