What are you going to do if I'm a criminal and decide to "taint" your Bitcoin by sending bits to your wallet? Sell your bitcoins?
I'm guessing you mean send some bits to one of his addresses. I suspect "taint" applies to txouts rather than addresses. He can avoid "tainting" his bitcoins with your bits by simply never spending your txout -- even though he has the private key.
Your comment reminded me of something you wrote earlier and quoted at the beginning of the thread:
Let's pretend I have one of Satoshi's wallet address and decide to send him a bitcoin. How can you tell which one is mine from his stash?
I can distinguish them very easily. The one from his stash was generated from the coinbase tx of an early block. The one you sent him is the txout of a much later tx spending some bitcoins you controlled.
An entire public history corresponds to each txout. These histories can be used to distinguish between txouts. That's why txouts are not fungible. This statement is often reasonably simplified to "bitcoins are not fungible."