If these sites are being seized with no followup legal proceeding, this is outrageous and should not be tolerated. However, if this is just step one in some sort of court case for piracy against an individual, fine. That makes it no different than getting arrested on the street, or having physical items confiscated with the later court case determining if you were right or wrong.
The larger issue may be, what the hell DHS and ICE are doing enforcing copyright laws.
Disclaimer: IANAL - anyone who has had their domain seized should contact a lawyer and not read lay opinions on the Internet.
If, has been implied, they are being seized under a Search and Seizure warrant (presumably as "property designed for use, intended for use, or used in committing a crime" - see Rule 41, Federal Rules of Criminal Procedure http://www.law.cornell.edu/rules/frcrmp/Rule41.htm) then there is no obligation for charges to actually be filed, but the owner of the domain name could move to have the property returned by proving that the property wasn't "designed for use, intended for use, or used in committing a crime" and was therefore unlawfully seized.
The larger issue may be, what the hell DHS and ICE are doing enforcing copyright laws.