A steady diet of such contributions alleviates my fear that this series lacks variety.
By "enemies of the Union" the Herald means, of course, insanely radical abolitionist Republicans.
In the Herald's view, they should be given no recognition, sympathy or support whatever.
They are the people, so the Herald believes, who will destroy the Union.
And to this very day, that's just how Democrats continue to speak -- they take their own very worst sins (in this case, the threat of disunion), and accuse Republicans of somehow advocating it.
It's like Obama, Pelosi & Reed accusing Republicans of "shutting down the government", when the decision to do so is 100% their own!