Practical considerations should not influence the legislation of an issue of principle.  Many laws have difficulties pertaining to implementation, but these do not diminish the strength of the principle behind them: people will kill other people, regardless of your legislating against it, but it does not follow that you shouldn't legislate against it. Even though the Netherlands had more liberal drugs' laws than in England, this did not lead, and nor should it have led, to a similar liberalization here.  As far as underground abortions are concerned, the problem is one of the implementation of the law. If the law were properly enforced, underground abortions would not be offered in the first place.