Price fixing is the result of collusion/collaboration, not of coercion.
The fact that the parties mutually benefit from their collusion, which is why they sought to price fix in the first place. It's an agreement like any other.
Please, just read up on the definition of price fixing. It'll clear these questions up for you.
Hence, it is not enforceable and the members will cheat on it, because the incentives are a Prisoner's Dilemma. Read about the PD, it'll help clear things up for you.
In general, I don't find price fixing that difficult a concept to grasp, which makes it challenging for me to break it down any further for you.
So, unfortunately, I don't think there's anywhere else to go from here. But, thanks for the discussion.