The Republic of Vermont constitution banned slavery in 1777. Vermont entered the union in 1791 and never had slaves while a state.
There are always some people who choose to ignore historical facts, such as the Vermont constitution banning slavery during the American Revolution.
Southern state's politicians deliberately instigated and full scale insurrection in 1860 in order to maintain and expand slavery, hoping European powers would send in foreign troops and destroy the Union once and for all.