The media has long fought sealed warrants, based on the First Amendment right of access. This right of access extends to judicial records, including search warrants and documents filed in support of search warrant applications. These have historically been open for inspection.
If less restrictive alternatives are available to sealing a search warrant, they must be used. Redaction, for instance, can allow for protection of "confidential informants" while still protecting due process requirements.
The reasons given for sealing a warrant can only be considered essential when the sealing of the warrant preserves higher values (common law rights) or is essential to a compelling government interest (constitutional right). The government saying that a warrant needs to be sealed for an "ongoing criminal investigation" or to protect the rights of a confidential informant should not alone be enough to seal a warrant. The interests of all parties need to be considered, including the "defendant". A sealed warrant prohibits the examination of the warrant by the defendant to ensure, for instance, that there is probable cause for a search. The sealing removes the ability of a person accused to challenge the warrant. Due process is, therefore, violated.
Without access to judicial records, constitutional rights become meaningless.