This isn't specific to euthanasia but applies to all prescription drugs.
I have no problem with saying that doctors shouldn't be able to use moral reasons to refuse to prescribe other prescription drugs, either.
What kinds of non-moral reasons should they use, then? Or should people be able to legally buy and use all legal medicine freely?
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.