Because, if you believe in the concept of "tainted coins", then that coinbase reward is "tainted" by the "tainted coins" used for the fee. It's as just as easy to trace as any other transaction that could have used those coins.
I don't believe in anything, governments do. Read the previous posts.
Sorry, I'll rephrase to avoid confusion:
Because if someone already believes in the concept of "tainted coins", then that coinbase reward is "tainted" by the "tainted coins" used for the fee. It's as just as easy to trace as any other transaction that could have used those coins.
What should a pool do if they receive fees from "tainted" coins? Cease operations immediately? Reject the transaction and let another pool mine it?
That depends on what the pool believes about the concept of "tainted coins". If a pool believes it's possible for coins to be "tainted", and that pool has reason to want to avoid awarding tainted coins to their participants then their only option would be to "
Reject the transaction and let another pool mine it". Anything else would subject them to whatever consequences they are concerned about.
Who are you going to trace exactly if you distribute the fees proportionally according to the hashrate submitted by miners?
If someone believes in the concept of "tainted coins", then (for them) EVERY UTXO created from that block reward is "tainted" (proportionally according to how the reward is distributed). There's nothing magical about coinbase transactions, the "taint" affects coinbase transactions in exactly the same way as it affects any other transaction.
The mempool is the only mechanism we have to mine transactions fairly.
There is nothing about "the mempool" providing any mechanism for "fairness". Each node maintains their own mempool however they want. The mempool is just a list of unconfirmed transaction that the node has not yet forgotten about. That's it. Nothing more.
Here the only incentive is fees paid.
That's the only incentive built into the protocol, but there is nothing about the bitcoin protocol that prevents any solo miner or mining pool from adding any other incentives that they want to add to their own mining. Some mining pools have already adjusted their transaction selection process, allowing users to "accelerate" transactions by simply indicating a desire to have their transaction included instead of a higher-paying transaction.
If we eliminate it, then any mining sector can implement any incentive they want, like "taint", "oligarchs first", "include Ordinals", "mine all of my own transactions", "deplatform exchange X"
All of those are already possible. A solo miner or mining pool doesn't need anyone else to change anything else about the bitcoin software to do any of those things. They can just modify their own software as they like.
and this will make transaction processing no longer decentralized.
The ability to make such modifications exists BECAUSE of decentralization. If Bitcoin were mining were centralized, then the entity in control could make any (or none) of these decisions, and then FORCE everyone else to abide by them. BECAUSE it is decentralized, neither you, me, or anyone else can decide what criteria a miner gets to use when choosing transactions.
