Tainting is the consequence of lack of fungibility. Fungibility is only achieved for coins those come out of Wasabi coinjoins.
UTXOs being called tainted is not the consequence of a lack of fungibility, but the consequence of the presence of transparency and openness of the Bitcoin blockchain. If it weren't transparent and accessible to everyone, including centralized services and blockchain surveillance firms, it wouldn't be possible to apply taintness, or it wouldn't make sense to do so. Everyone is free to join, observe the current state of the blockchain, do some research and come to certain conclusions based on subjective values and arbitrary interpretations of reality. The problem is that
my subjective interpretation won't make someone else's coins illegal, nor will it make them less valuable or non-fungible.
Your subjective interpretation will because you're running a centralized service that decides who can enter the system.
Fungibility: indistinguishability is achieved on coinjoin outputs, as receivers of coinjoined coins cannot make meaningful differentiation between any two coinjoined coins.
Conjoin makes outputs indistinguishable from one another, but it doesn't make them fungible because you can still differentiate between non-coinjoin and coinjoin transactions. What if "they" call all coinjoin transactions tainted? What will zkSNACKS do in such an unfortunate case?