The fungibility of Bitcoin — Long Term

The fungibility of Bitcoin is a serious topic that requires discussion. I hope we all agree that having our transactions publicly announced won't make ours coins fungible. Truth be told, our beloved Bitcoin can't work same like as cash, because cash doesn't leave footprints. A dollar is equal with a dollar no matter who transacted it with who. On the contrary, a block chain analysis may be enough to prove that my inputs have a connection with a criminal activity and be censored for that. Recently, I read that despite the mixing and the coinjoining, there are centralized services that will decline “tainted” bitcoins.

It then comes to my mind that once there will be really less bitcoins left to be mined, like two decades later, the miners will have a better income from the transaction fees instead. Right now, every 10 minutes, 6.25 freshly mined and “whitelisted” bitcoins are brought into circulation. But, after we've mined most of them, we'll use the already mined bitcoins for our transactions.

If that's true, then the system will be filled with “tainted” bitcoins in the long term, as there'll always be criminal activity. Your thoughts.