Can (a part of) the constitution be declared unconstitutional?

[True Federalist (진정한 연방 주의자)]

In your specific example, even if a Court were inclined to rule the 14th Amendment could be interpreted that way there are two other bars. Article V requires that any amendment denying each State equal representation in the Senate requires every State to ratify it and there never has been a time that was the case. But even ignoring that, the 17th Amendment reaffirmed each State having two Senators.

It did take several decades before the Court started interpreting that the 14th Amendment incorporated the Bill of Rights so that they applied to States.

[True Federalist (진정한 연방 주의자)]

The combination of the 5th Amendment to the US Constitution + The initial Constitution ban on bills of Attainder (for both states and the federal government) + the lack of US Constitution specification on how someone could become a slave would have been used to declare slavery unconstitutional in the 1790s had we not had an activist judiciary.

The Federal Constitution had no need to specify as how someone became bound to a term of service would be defined under State law, not Federal. Moreover, you show an appalling lack of knowledge of the scope and purpose of a bill of Attainder.