Sabotage is a useful technique in wartime. The CIA (the the OSS) investigated something like 15,000 supposed acts of sabotage in the US during WWII. (I don't think they found any that were actual sabotage).
They'd want to promote sabotage in Axis countries, and to prevent sabotage-like activity in allied countries, as much as possible.
The OSS would have been carrying out operations overseas. The FBI would have been investigating sabotage or suspicions of sabotage in the US. The Germans actually landed some agents in the US with plants to blow up this and that, but they were all caught before they could do anything.
You could argue that perfectly loyal American tank and torpedo designers accomplished a lot more than any Axis agent could have hoped for.