Yeah, I understand that anything can be used for the wrong purpose. With FIAT and BTC, you can investigate transactions without interacting with each address owner on the blockchain.
However, if the FEDs want to investigate a transaction through DRK, they have no choice but to go after the master node. Even if you did nothing wrong, you will have a chance for the FEDs to poke into your life.
Investigating a transaction via the MN will get them nowhere, even if they could figure out which MNs were involved in making it. They'll figure that out relatively quickly. Although that doesn't mean they'll stop intimidating you I suppose.
Yet another reason MNs should be hosted outside the US/EU with a non-American company.