"Following the line of thought that has been established here, I would like you to prove that the institution of slavery was the heart of the matter. Because people did not want slavery or slaves in their state, isn't it possible that simply meant blacks?"

Many northern whites wanted neither slavery or blacks in their communities. That meant both slaves as individuals and slavery as an economic, political and social institution. That is why northern whites often opposed slavery as an institution...but not for the benefit of blacks.

Slavery was still at the heart of the matter, for without that institution (and people wanting to extend it), the issue of a "black" presence in the states and territories would not have existed.