The “inherent bias towards freedom” comes from the Bill of Rights, which was adopted later, and from the balancing of power against power in the Constitution itself. If the Congress that passed the Bill of Rights thought secession was important, they would have written it into their amendments. The convention of 1787 didn’t write it into the constitution, and the “inherent bias” of the Constitution towards checks and balances suggests that an absolute right of secession on demand was not part of the Constitution.