Recently there was a question on this site regarding whether parents should be able to kill their disabled children:
I'd like to flip that question around and ask if disabled children should be able to kill parents who articulate a desire to kill them. Ableism, like racism and sexism, is a violent social phenomenon that is perpetuated by attitudes like the ones articulated in the "yes" section of the latter question. Certainly this poses a burden on future generations who are indoctrinated into this kind of thinking. Hence, do those who support killing other people groups have a right to live, or does the danger they pose to the lives and well being of oppressed people outweigh their claims to a continued existence?
I would love to see my parents on the other side of the door while I talked to their doctor about putting them to sleep, just to get them out of my hair, the same way as they handed me over to a Home for the Handicapped so they could get on with their lives, and not be embarrassed by me when having friends over.
You ask, "why is it ok to kill disabled infants but not ok to kill people who support this?"
I presume you're referring to this : [http://www.Debate.Org/opinions/should-a-woman-be-allowed-to-abort-if-their-child-is-disabled] but your link didn't work correctly.
The answer is because your premise is flawed. It is not ok to kill disabled infants, and this doesn't happen (legally, anyway). What you're referring to is aborting a foetus that has tested positive for some form of disability. A foetus cannot consciously choose to kill its mother while inside the womb, that's ridiculous.
Unless there is a threat to your life or that of others, you cannot kill another person. If you can remove yourself safely from the situation without much effort, you cannot kill another person (in most states). Articulating the desire to kill someone is a threat, but not a significant enough threat to warrant self defense. Moreover, any planned killing is usually never granted self defense protection because the person could have removed them self from the situation. Just because it is morally wrong doesn't mean the criminal deserves to die. Yeesh.