Interesting exercise in opinion.
However, the issue is not the Tenth Amendment when referring to that conflict of the 1860s; the constitution adopted by the seceding states made that utterly plain.
So, now I am supposed to believe that the words of the Founders who said what the Constitution meant when they ratified it meant nothing, but were only their "opinions?" The end result of your logic leads to the Living Constitution where politicians can alter interpretation of the Constitution to have it mean what they want it to. It may be your way of interpreting history, but it is not mine.
Please explain what you mean. The Tenth Amendment was/is part of the US Constitution. It applied/applies to all states in the Union. Explain to me how it doesn't apply to the right of a state to secede.