Just like how it is impossible to filter out tainted fiat currency then it should be similar to bitcoin since we have mixers and other means of making bitcoin transactions more anonymous and It's just hypocrisy seeing some coins flag while in the blockchain they are all the same because this makes bitcoin Fungible as a currency

A similar situation is that I as an individual may choose not to accept my local fiat maybe cause how old it looks but when taken to the bank it will definitely be accepted.

We don't always have to know who once used our fiat currency or what they did to get it before we can use it which should be a similar situation in Bitcoin.