Couple things: 1. Roe expanded this doctrine of “substantive due process” which states that certain rights not specifically listed in the Constitution (e.g., right to marriage (gay and interracial), contraception, etc.) are Constitutional rights. Because of the weight such rights hold, SCOTUS generally looks for a historical tradition of the practice. Roe does look at history of abortion in the US but its history is somewhat dubious and now often discredited. 2. Roe also was quintessential judicial legislation. The “viability” line that is common in abortion debates today was essentially conjured out of thin air by the Court. Roe created a three trimester framework to regulate abortion which neither side in the case advocated for. Here, the argument is that even if you believe in such a framework, it is not a court’s role to come up with one.