3/5 Rule

Framers of the Constitution included a rule to count slaves for purposes of creating a democratic republic.

Every non-slave was counted as one person in the census; however a slave was considered 3/5 of a person. This rule was later repealed in the Constitution and today everyone is counted as one person.

But this is a crucial argument used by those that do not approve of the Constitution and its framers. The founding fathers created an erred document that dictates our government today. Therefore any document that once contained the 3/5 rule has had errors in the past and today's attempts to remedy "faults" in our republic are justified.

Questions:
-Why was the 3/5 rule included in the Constitution?
-Are the framers "Racists" for utilizing a 3/5 rule?
-Does the fact that Constitution was later changed justify a polictician creating a policy that is unconstitutional?