[Frieza_Prexus]

You can make whatever decisions you want for yourself. There is no right to end the existence of a third party. You don't get to make the call because no one can. You're basically framing the argument as if children were property. Parents are guardians of their children not owners.

To address your addendum: you're essentially justifying the killing of any mental incompetent. Mom's got Alzheimer's? Don't worry; I have a gun. You may think there should be a right to do so. Many do, but no amount of gymnastics can divorce the act from its definition. You are morally justifying the death of people whose existence you personally find inconvenient. No one can make the determination about the worthiness of a life but the one living it.