While I agree that Sony promised more than they could ask for, the hacker(s) involved in this acted too negatively to this, IMO.
Sony removed the ability to install OS systems on the PS3 for a reason; most likely to improve it's ability to actually PLAY games. This seems reasonable enough, so I don't see the (legal) motive of the hacker(s).
tl;dr Sony tries to make game better, hackers get mad that they lose one simple feature.
The PS3/PSN was officially deemed (legally) un-jailbreak-able by the Sony corporation. IMO, this was a step in the right direction to prevent further hacking. GeoHotz had not obeyed this, and was subject to a (possibly large) lawsuit. Seeing that they could no longer obtain illegal copies of games, the hacker(s) were affected negatively; but the error in this situation was that they protested against Sony for not allowing them to do such. This seemed immature.
tl;dr
"OH Q_Q SONY SAID I COULD USE LINUX, AND I USED IT FOR PIRATING BREAKING THE USER AGREEMENT, AND NOW THEY TOOK IT AWAY AND I'M THE ONLY ONE WHO GIVES A stuff ABOUT IT SO I'M GONNA forget IT UP FOR EVERYONE ELSE"
My observation, in short, sees the hacker(s) as the one(s) in the wrong because he/she/they did not consider the legal implementations, and seemed to only be concerned about having one feature of the PS3 system.