Yes, violent insurrection against the lawful authority of the Crown is no laughing matter. (And many of them were slaveowners, so they did not have moral authority neither by the standards of their day nor by ours.)

It's ambiguous. The concept of slavery being bad was quite novel and mostly comes from English philosophy/legal theory which America has a direct lineage from.

The German immigrants rejected slavery a lot more vigorously than the English who had been there for a bit longer.

Interesting if true. Regardless, I'd just expand the general net to a European philosophical lineage.