After all virus writers/crackers/spammers are just business too.
Just because its government that hacks you doesn't make it any better, I believe it makes it worse.
--I know it's illegal (except if a big company like Microsoft or a government agency like the FBI does it). It's the dream of every information security professional though.
Counter hacking is just hacking, the only difference is how you pick your target. And you never know, maybe the owner of the originating system was just another victim. (Hacker breaks in computer A, then precedes to hack computer B leaving trace back to computer A, not the hacker)
It is also against the law in most of developed world.