For the mainnet it's fungible, for CEX/AML/governments it's not.
You either accept both Bitcoin and Monero as fungible, or you blacklist the former and delist the latter (due to your inability to track it).
You can't expect they will use their common sense because they're using double standards.
If you received coins that they said "dirty coins", your coins will be frozen and you will be asked many information, but in the end you can't access your coins.
But if they i.e. Federal Reserve confiscate the coins from criminals, they can auction the coins and they will earn money from that. Federal Reserve is actually a legal mixer since they launder from "dirty coins" to "clean coins".
That's a really good point.
Silk Road bitcoins were deemed "tainted", until the US government decided they're not and started selling them.

Voila, you now have "clean" bitcoins!
Maybe they want to have a
mixer monopoly too.

Well, fiat money is considered to be fungible, yet it has the same concept of taint. Entities like banks or some companies can freeze and reject transactions if they deemed as high risk by their algorithms, for example coming from a blacklisted country. Or when a person with no financial history suddenly deposits a huge sum in cash.
This is the reality of digitalization. It allows much easier control on the monetary flows than physical money, and governments don't want something digital yet anonymous like Monero to be widespread, so they will never allow it to be accepted by legally operating businesses.
Even physical money cannot always be considered fungible...
Banknotes have serial numbers for a reason.
Only metallic coins (either gold, or fiat money ones) can be considered truly fungible, since they have no serial numbers by design.