Well, that is an opinion based on the result of a war.
As Ben Franklin said "Force sh*tes upon Reason's back."
Whatever eloquent argument one might make for the legality, constitutionality, etc., of a particular act, it really boils down to who has the ability to use force to enforce their desire.
Heck of a way to run things, but there you go.
My belief is based upon the thoughts of the Founders and the meaning of a “constitution” not the result of that little dust-up of 1861-5.