Laying down a principle that states cannot be interfered with at the federal level in legislating to protect abortion is NOT legislation.
What you falsely define as a "principle" implies it cannot change. This isn't catholicism, but law. Laws change all the time. A ruling is not a principal.
Rulings are based
on the current laws. Tomorrow, new laws can be passed and past rulings can become obsolete.
SCOTUS present-day rulings, depending on how they're worded, can PRECLUDE future laws. They lay down legal principles and precedents.
This is only true if there is a lack of legislation...or if the legislation isn't clear.
You're basically arguing that SCOTUS is more powerful than Congress. That's not the case at all.