Isn't it normal for police to seize evidence in cases like this? Your comparison doesn't seem very helpful, as there is a big difference between holding someone at a police station vs seizing evidence.
I admit there is a big difference between someone's property and someone's liberty. However I still don't feel it's justified to potentially invade thousands of other user's privacy in order to gather evidence, especially since they could have subpoenaed him and he has a history of complying with such requests.