Anyone trying to secede would be painted with the "Confederate"/"Racist" label. There doesn't need to be truth behind such accusations, they just need to repeat it ad nauseum.
They would be false. The underlying impetus the last time was the moral imperative of ending slavery. It no longer exists.
Was the right to secede ever resolved in court?
I don't believe it can be done by force, but why would a predominantly liberal north want to stay with a predominantly conservative south?