There are a myriad of things that are legal for the government to do that are illegal for a common citizen. There's no irony in that.
Weev didn't hack anything. He committed data theft and possibly attempted extortion. Those should be the the basis of his trial.
Also, just to be clear, those things are actually quite illegal for the government to do both on a national and international scale.
If the government does not require a warrant to do something, then it should be legal for anyone to do. After all, the entire purpose of a warrant is to insure oversight in the use of government power.
The government doesn't require a warrant to prevent people from entering or leaving the country.
The government doesn't require a warrant to block off city streets or do any of a number of things to public property.
The only things that the Constitution requires the government to get a warrant to do are "search and seizure", which are terms with very specific meanings in the Common Law. The NSA somehow argues that intercepting people's traffic isn't a "search" until an analyst actually looks at it, which I think is a ridiculous argument; however, the response isn't "everything you do needs a warrant", but "that's a search, and searches need warrants".