Why is it politically controversial to say the Constitution is imperfect?

Hmm... maybe you should specify. I mean.. the whole point of the Constitution is that it can change with the times... so obviously, if it can change (the whole bill of rights and all) then it is made to be able to evolve to future needs.. meaning that it was lacking, and imperfect... and since change is not perfect itself, the Constitution can't be perfect... rather it is always a work in progress that seeks perfection in an imperfect world... or something like that.