This tactic is misplaced. You don’t outlaw abortions because the fetus is evidence of a crime, you outlaw abortions because killing children is murder.
This law would only protect unborn children because they are a useful tool to prosecute rape. Normally conceived children would be assumed to have no value.
When the prescription is too cute by half and easily opens up to ridicule the side supposedly being helped, one has to wonder if we are dealing with a counter-agent.