There is nothing wrong with the tainted coins if you can spend it. The coin from exchanges are also tainted.
However, companies may reject those kind of coins. For example, Bitpay has allegedly[1] warned the merchant about the blacklisted coins and it makes no sense whatsoever. Almost all the coins are tainted in someway and Bitpay would be marking majority of the legit transactions as a fraud.
[1] https://www.reddit.com/r/Bitcoin/comments/3mea6b/bitpay_is_blacklisting_certain_bitcoins_rejecting/
I don't get it either... And the more time passes, more and more coins will be tainted somehow.
The exact same thing happens with fiat as well.