@roger,
It should only be allowed when it is established scientifically that human life does not begin at conception. Legal wordplay notwithstanding.
It is not sound policy if it does something to us all which should not be done. I realise that the "should" implies a moral position but who we are is an entirely moral position. Also, what should not be done cannot be judged when the reasons it should not be done are not fully understood, or hardly understood, or not understood at all, or on Ignore.
We have an excuse for that, apart from the last, because of the mass psychological complexities involved, but I hardly think USSC justices are allowed to use it. Diluting a sense of the sanctity of human life and of romantic love are not small matters.
We demonstrate that sense by hiding abortion from view just as we learned to hide executions and by not talking about any real abortions in any adult manner and using the word abstractedly just as the Soviets used "administrative liquidation".
Our mass shame about abortion is palpable. And rightly so.
The anti-abortionist can go before any scientific peer-group and demonstrate that human life begins at conception and that the life does not give a tuppenny-damn how it got here. what anybody thinks about it or what sort of condition it is in. Just like an infant. It has one great instinct--to survive.