If you want to liken this crack to something, it wouldn't be knives. It would be something like lockpicks.
While a set of lockpicks is arguably something that you might want to keep around the house for non-criminal purposes - say, helping out a buddy who locked himself out of his house, for example - they can also be used to commit crimes. And there are a lot more people out there who'd be interested in using them for illegal entry than there are people with a legitimate reason to own them.
Posting instructions on how to crack the PS3 on the internet like that was like handing out lockpicks on a streetcorner, no questions asked. You know there are a metric crapton of people out there who are going to misuse them, and that they arguably outnumber the people who would only use them for legal purposes. It's just an irresponsible, asinine thing for someone to do. You can't tell me that this guy didn't realize how this information would be (mis)used once he put it out there. And his actions don't just hurt Sony. Piracy can lead to publishers cutting back support for a platform, and online cheating sucks for everyone who's interested in legit, exploit-free play. For the people who bought their PS3's because they want to play big-budget, commercially-developed games (which I suspect is the majority of owners), 'Hey, devs may put less games on the system from here on in, and you'll have to deal with a lot more cheating and hacks when you're playing online - but that's OK, right? I mean, you can run homebrew now!' really isn't cutting it.
For the record, I think Sony overstepped their bounds with the attempts to subpoena the Youtube and Twitter info. Two wrongs don't make a right, though.