I don't see why pro-lifers should have to 'leave' this board. As long as they are not being argumentative and imflammatory then I think their opinions and advice is just as useful as a pro-choicer's (to whom the same rules apply). Obviously, if someone is writing to say they are certain they want an abortion and want to know about procedures and stuff then it would be inappropraite for a pro-lifer to tell that person that they are evil and wrong etc.
However, if someone wants advice about what to do in their circumstances of, for example, an unwanted pregnancy, then a pro-lifer has as much right as a pro-choicer to respond on this board.
Everyone just needs to respect each other's opinions, not stoop to childish name-calling and most of all, be supportive and helpful to the original poster.