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.
Interesting point, but Vermont was not a state. It did not vote on the Constitution's inception as the new law of the US.