Note that this isn't about exchanges freezing funds owned by drug dealers, that's understandable. It's about freezing funds from the bar where the drug dealer bought his coffee.
Do you have any evidence that this is happening?
No, it was a theoretical example.
I don't think it would be difficult for a blockchain analysis company to see the difference between someone buying $100 worth of drinks at a bar, and a someone selling $100,000 worth of coin.
The $100,000 might get more interest, but does that mean the "taint" disappears for small transactions? It sounds arbitrary.
And what if the miner gets a transaction fee from a drug dealer? Or if the drug dealers pays a very high fee to a friendly miner who gives him back fresly mined coins?
I think you are conflating multiple issues. Blockchain analysis is going to reveal that a hypothetical drug dealer paid a bar $100. That same blockchain analysis is going to reveal that it is some merchant receiving that transaction for a nominal amount. Exchanges are generally not going to care about a merchant receiving nominal amounts of coin from a drug dealer, when the amounts are in line with what they expect to receive during the normal course of business from a single customer.
The above is similar to a drug dealer paying a transaction fee. If the fee is within an expected range, no one is going to bat an eye when the miner goes to spend the block reward. However, if the transaction fee is outsized, questions might start to get asked, especially if a particular miner receives large transaction fees on any kind of regular basis (when other miners do not).