That is correct in the sense that the U.S. Constitution makes no mention of secession. Thus, under the Anglo-Saxon legal principle that "all is permitted which is not explicitely prohibited", secession is permitted under the Constitution.
I and others on numerous occasions have carefully and patiently explained to you why the Militia Act of 1792 or its amended version of 1795 does not apply in the case of states that have seceded from the Union. It would apppear to be pointless to go through that again.
Laws are enforced by power, in this case military power. No state can get out of the Union unless it can fight its way out. No state has been able to do that.
No state has ever been out of the Union for single second.
You should be glad that President Lincoln always took this as a starting point. As soon as the so-called seceded states published their secession documents, many in the north (including Frederick Douglass) lobbied to have them branded as traitors who had forfeited their rights as citizens; further, according to this reasoning, their property could be seized.
Later in the war, it was proposed in Congress that the insurgent area be broken up into military districts. President Lincoln also resisted this initiative.
Walt