In Canada, doctors are not allowed to kill patients; only to assist those patients in committing suicide.  There is a difference.  
Adults have the right to make choices about themselves.  We may disagree with those choices and believe that they are wrong, but the choice belongs to the person in question.  Giving a person a choice is not the same as "delivering a person to her/his death".  It seems to me that by assuming responsibility for that patient's ultimate decision, you are, in a way, trying to exceed God, since even God gives us free will.   
Children must be guided by adults.  If adults guide them to cocaine dealers, that is not good, because a child cannot always be expected to make a soundly reasoned choice.   It would be the same if one were to lead an addict to a dealer, because the addict is not making sound decisions.  
A terminally ill person may or may no be capable of making sound decisions, depending on the given circumstances.  That's why they consult doctors.