I am not a specialist.
In my memory, the relationship between Secession war and slavery is complex.
South seceded because it was afraid that Lincoln would end slavery. North made war to prevent secession.
The abolition of slavery became an official Union war goal on January 1, 1863 with Lincoln proclamation, not before, for many reasons, one of them being to confort relationships with Europe.
That does not mean that Lincoln did not want abolish slavery, but that he was reluctant to do it at the beginning of the war, for political reasons.
Gettysburg and the victorious end of Vicksburg siege opened the way.
Back to the topic, the decision to wake war does not make Lincoln a fascist, and did not make him ultra-left, even according the standards of the times. .
And what if theses people wearing nazis symbols are showing signs with racist slogans, calling for the death of Jewish and black people, giving tracts with the same propaganda.
A hint : in most European countries, it is a misdemeanor, punished by law, and strongly.
The article is not very good, but gives insight.