[the OlLine Rebel]

No, it wasn’t. Secession wasn’t in question. Whether it was wise or nice was.

And no qualms about secession within a state when it came to parting out West Virginia during the CW. But now we’re told that’s not “allowed”.

[BroJoeK]

the OlLine Rebel on whether secession was treason: "No, it wasn’t.
Secession wasn’t in question.
Whether it was wise or nice was."

Nonsense -- President Madison moved troops to put down rebellion in New England, if necessary.
Rebellion & treason are the same thing -- see the US Constitution Article 3, Section 3.

"...Jeffersonians described the [Hartford] convention as "a synonym for disloyalty and treason", and it became a major factor in the sharp decline of the Federalist Party.[46]"

the OlLine Rebel: "And no qualms about secession within a state when it came to parting out West Virginia during the CW.
But now we’re told that’s not “allowed”."

More nonsense -- lots of states have changed boundaries or split off from others, Maine comes to mind splitting off from Massachusetts in 1819.
The key fact about all such changes, including West Virginia, is that they were done by mutual consent of all the parties -- the old state, the new state and the US Congress.
Did you ever hear that term, "mutual consent"?
So long as everybody agrees & follows Constitutional procedures, we can do what we want.