You said, in essence, that Blackmun's postulated scenario was the only "legitimate basis" for overturning Roe. That's just wrong. There is PLENTY wrong with Roe quite aside from this issue, and I will tell you this; if Roe is ever overturned it surely won't be on these 14th Amendment grounds.
The only alternative is to argue that the right to privacy does not exist, simply because it is unenumerated, which would violate the Ninth Amendment.
That is illegitimate because if your crusade is against privacy, you would attack the precedent on which privacy was established pre-Roe. And yet, you target Roe and not those cases. Why? Presumably, because there is a child's life involved.
It is the taking of a child's life that makes us disturbed by Roe. The issue then comes down to whether that life has a right to exist or not. The very foundation of our nation states that it does. The child has the right to life equal to our own.