“The Bible gives clear, direct guidance on many topics of morality, but not on birth control. Thus, any inferences from the Bible are opinions and not Biblical evidence.”
Where the subject of the morality of birth control is concerned, this quote from the Christian Bible Reference Site is probably as good a place as any to start.
The question it raises in my mind may be framed different ways. One way: Are direct commands from God our only real source of unambiguous moral guidance? Another way: Do inferences drawn from established biblical principles really constitute such an ephemeral and debatable source of spiritual direction that God may as well have given us nothing at all to go on?
In short, what exactly constitutes legitimate biblical evidence?