Yet again. You seem to lack a basic understanding of the difference between if and iff (if anf only if).
If does not imply iff.
I have a basic understanding of implicature. Saying that you are permitted to kill patients if you are doing it incidentally in the process of alleviating pain also implies, in normal conversation, that you are not allowed to do it otherwise. It is a "limiting implicature".
Over at Scott Adams' Blog you can find a very fine example of using the 'Rationality Engine' to solve the social problem of assisted dying.