The US system is founded in innocent until proven guilty in a court of law. The requirements for this proof have been laid out and refined over 200 years. I think those requirements are not strict enough, but these seizures don't even include an actual trial, and thus deny the victims the right to defend their position, or make their case before a judge.
Earlier this year I heard about a hip-hop blog that was seized which engaged in no piracy... though it did offer songs that the record companies had given him as a form of promotion.
So, not only is this being done without due process, but it is being done incompetently to boot!
I have zero expectation that this won't become-- like the "drug war" and the "war on terrorism" -- an ever widening net to where it effectively becomes seizure of politically-incorrect domains (e.g.: write a post critical of the government on your blog? have no blog the next day...)
This is literally a form of government censorship of speech. Even if some speech is "illegal" (I don't think even pirate spreading domains are illegal, though there is a good civil case against them) the act of speaking is protected, and this right is acknowledged by the first amendment.