Allowing FBI to have any more control than they already do is bad.
It is similar to owning too much of a network, and a good example is 51%+ threats to Bitcoin.
This doesn't just mean Bitcoin networks, all networks in general.
FBI has enough power, they should not be allowed to gain more resources/power with these seized Bitcoins.
I will be using a Bitcoin tracking device to make sure I never get Bitcoins that the FBI once had and I will be able to track every company/person that accepted them.
This is very easy and possible to do.
We as a community can reject these coins all on our own.