The right to self-defense there was seen as deeply rooted in our nation's history and tradition; thus, it was a fundamental right.
Many fundamental right are protected by both Substantive Due Process and Equal Protection.
There is no big difference in the analysis
Fundamental rights under SDP focus on determining if there is a sufficient governmental purpose, whereas Equal Protection focuses on whether the government's denial of the right to certain people is justified by purpose.
The Role of the 9th Amendment Here
Doesn't protect rights itself; rather, it justifies the existence and protection of unenumerated rights.