I mean the 9th is just one of the arguments justices have made in the past. Arguments for incorporation and privacy rights have cited The 14th Amendment Due Process clause, the 14th Amendment’s Equal Protection clause, 14th Amendment’s Privileges and Immunities clause, the 4th amendment, the 5th amendment, the 8th amendment, and the 9th. Personally I have always liked the argument for the 9th amendment protecting unenumerated rights, it makes logical sense, it’s not the primary backbone for the rulings, there were several different arguments from the justices incorporating various pets of the constitution. Which makes sense; the “penumbra” of rights to privacy are definitely there implied under many rights- protection against search and seizure, speech and assembly, protection from self incrimination, due process, privileges and immunities, and even the 3rd amendment’s quartering act is affording privacy to American citizens.