Advocating secession is, was, and never will be treasonous. The original poster of that falsehood knows that it's a falsehood, and it's just one of many.
Justice Grier in the majority opinion in The Prize Cases refers to the secessionists as tratitors.
Walt
"Justice Grier in the majority opinion in The Prize Cases refers to the secessionists as tratitors."
Then why were they tried as traitors?
Ping to the Constitution!
It's the reason there was never a trail.