Seeing as though doctors have shown their willingness to rip unborn babies to bits, it's not a stretch to believe that there will be doctors who might shoot up somebody's grandma with poison.
Point taken, however, abortionists are relatively rare, hardly the rule.
The arguement that doctors are waiting to rake in bucks offing gramma is, imo, more grasping at straws by opponents than anything else. What prevents doctors from doing that now, personal ethics or the law? I'd say that the law won't stop a determined murderer.