There's 2 arguments really.
There's the argument that "no matter how foolproof a system is, it's still hackable", in Sony's favour. Yes the hackers are at fault, but it goes without mentioning that they're pricks, as it's so obvious.
There's the other side that although any system is hackable, it's arguable that Sony are at fault for not putting in place enough preventative measures. Various sources have implied that Sony's security was severely lack, potentially due to them relying on the hardware rather than using any software encryption. In fact I'm fairly certain I read on this very website that they didn't even have any firewalls.
The fact of the matter is the consumers trusted private sensitive information to a corporation, and that corporation let them down. This is fact, not opinion.
People like the OP are too eager to bend over backwards and accept corporate bullshit, and this is why many big businesses get away with such things these days.
Consumers need to go back to demanding better service.
"Oh but isn't PSN free?". Well if someone's used their credit card details then they've obviously paid for something. How would you react if paypal or amazon leaked your credit card information? Just because something isn't subscription based shouldn't mean it should be slack with security.
"Haha this is why Xbox Live is better and deserves to be paid for, they keep information safe". We shouldn't have to pay for security in regards to sensitive information. That should be a given anywhere you pay for something. Saying Xbox Live fees are acceptable based on those grounds really is the sign of a really dumb and spineless consumer.
The only extra features that gold members get that incur any cost towards Microsoft is the chat feature. That's all. I'll take skype, teamspeak, xfire, any of those really.