Truth is always the best defense. You can read what it says in clear and simple language.
It protects slavery. I believe Lincoln himself says in his first inaugural that Article IV, section 2 does in fact protect slavery. If you like, I'll go check and if I have remembered correctly, i'll give you Lincoln's words telling you the same thing that i'm telling you.
Perhaps Lincoln's words are the best i've got. I'd say for most people, the mere text is good enough to grasp the meaning.
"It is scarcely questioned that this provision was intended by those who made it for the reclaiming of what we call fugitive slaves; "
He says some more stuff you won't like on the other side of the above link.
I know exactly what it says. It dealt with more than... “persons held for service or labor” ...Compromising in the present does not mean the future would be the same. I also know that the section addressed other people than just them.
Why do you think Congress would have been able to act after 20 years?
Why do you think that the importation of slaves could be prohibited?
It is clear that the Founders were ashamed to even use the word “slavery”, most believed it would die a natural death as the nation evolved economically.