Bitcoins are fungible, and luckily, will ever be.
Is there even a DB to check if the BTC you just received are tainted and if so with what activity ?
How would you feel to be sent back BTC stolen from you to make a purchase. I'd wish to do some investigation.
You are mistaken. Bitcoin fungibility is NOT debatable.
Yes, the history of how all coins change ownership is available but that's all there is because it's impossible to accurately and reliably link it with actual identities or activities. Yes you can do it roughly, but not 100% accurately and 100% reliably, and that pretty much sinks your point.-