With a community-wide awareness of "taint", exchanges, merchants and services would start rejecting transactions containing "tainted" inputs, making it harder for the user to spend or sell those coins, and therefore have lower value than "untainted" UTXOs.
"Tainted" coins are not harder to spend. Just because someone tells you your coins are worth less does not mean they really do. They worth exactly the same as long as you do not interact with folks who mistreat bitcoin.