you can interpret this as a problem and as a solution too. Yes, ztransactions will could dye your money so no exchange will accept it because you are a terrorist and the US can ban the usage of ztransactions. In my opinion it's better like this, since the overall goal is to not rely on exchanges and regulatory thirdparties. In a P2P economy (which is this technology is meant to lead us) fungibility problems are not a thing beacuse there is no relative central party to make a standard.