It's the government trying to enforce their opinion of who should own those Bitcoins, thereby taking power away from the owner that the network has decided on, which would be "whoever has the cryptographic keys".
To secretly monitor a single individual's communications, law enforcement should have to get probable cause, present their case to a judge and obtain a court order.
Dragnet surveillance of all communications all the time is a Very Bad Thing.
Financial surveillance and seizure is currently at the Very Bad Thing stage and bitcoin helps move us back toward a better balance between the rights of the individual and the interests of the state.