It is true that sometimes you learn something at time T2 that invalidates something you learned at time T1 (T2 > T1), and thus you do need a de-ratcheting system of some sort.
But what actually drives the ratchet is experience with current policy (or lack thereof). "Oh, we had no plans to deal with X, and we got screwed, so lets add policy for X".
The ratcheting aspect of policy reflects the ratcheting aspect of societal experience accumulation.
Experience.
It is true that sometimes you learn something at time T2 that invalidates something you learned at time T1 (T2 > T1), and thus you do need a de-ratcheting system of some sort.
But what actually drives the ratchet is experience with current policy (or lack thereof). "Oh, we had no plans to deal with X, and we got screwed, so lets add policy for X".
The ratcheting aspect of policy reflects the ratcheting aspect of societal experience accumulation.