I think your overwhelming trust in arch-conservative lawmakers to make sensible exceptions in certain cases is severely misplaced.
Who says it would be overturned entirely by arch-conservatives? They would likely need to concede exceptions, even if they didn’t want to.
For argument’s sake, let’s say it became illegal in all cases. Still, it’s hard to imagine that more halachically mandated abortions would be prevented than ones that are halachically proscribed.