1) I support prison abolition, yes.

2) What is or isn't de facto slavery is worth discussing but we should certainly move towards removing de jure slavery.

3) I don't know the intention of framers of the constitution in choosing the word slavery, but it is the word they chose. So unless you mean "reactionary" very very literally, using it to describe advocates for a progressive cause interpreting a word well within its historically normative meaning is at best slick rhetorical judo. At worst an indication of bad faith.