1.) Computer virus runs rampant at a previously unimaginable speed, creating problems nationwide.
2.) Chinese/Nigerian/Russian/Alien? hack attack on U.S. information interests.
3.) Silence internet communication in the event of revolution/uprising/secession.
Seeing as how people are openly questioning gov't expansion these days, #3 might not be too far off the mark.
1) So let the govt write an open source anti-virus program and offer it for free. If it's open source, folks can check it for backdoors and whatnot. Less work than you think, as ClamAV already exists. Fork it or improve it, and give it the US govt stamp of approval. Done.
Similiar idea, create a better patching solution. Open source it, done. Between the two of them, you solve 60% of the computer security issues of the entire US.
2) So specify control over the undersea fiber lines, not domestic networks. Technically, the govt has darn near unlimited rights to do as they please when it comes to the border. Not saying it's a good idea, just a probably Constitutionally ok one.
3) Yea, that's my take on it. Censorship or whatnot rather than security. That's the purpose of most govt security programs.