It is exactly what you are doing. You won't apply your 1865 morality to the Founders, but you INSIST on applying it to 1861.
1861 is still prior to the fact.
Again, morality is the same, whether it’s 1861 or 1865 or 2015.
It’s wrong to enslave your fellow man.
It is wrong to rebel against legitimate governmental authority without an overriding moral basis.
And it is wrong to strip the sovereign People of the United States of their national territory, without their consent.