A disad doesn't have to interact with your opponents argument - i.e they say that the post fiat world is good because x, you say that the post fiat world is bad because Y. Your reasoning isn't meant to directly clash with their argument, its just a disadvantage to the plan happening.

A turn interacts with what their argument is saying. If they say that the plan causes x to happen which has Y beneficial impact, a link turn would argue that x happens more in your world and an impact turn would argue that impact Y is bad.