They can voice it perfectly well. The problem is that they can't be heard in the mass media without some large event to draw attention. The last month has been their big event, and now they have the attention they needed. They had a good plan and it was executed perfectly.
[Edit: by "good plan" I mean that their plan had a good chance of success, not that it was beneficial. That part is still up for debate.]
No, they cannot voice it perfectly well, if they have to resort to stealing user information to get their message across.
Their plan was not good, insofar as it caused pain for a great many people. What they did was not okay, and should not be lauded as a positive thing for the Internet at large.
The problem is that their antics are even being considered as anything other than the terroristic (in the real sense of the word, not the post 9/11 hyped up nonmeaning it tends to carry today) acts that they are.
If someone broke into a hospital and flung all of the patient records out onto the street, we wouldn't be having this discussion; they'd absolutely be considered criminals. So what if the glass they broke to get into the hospital wasn't shatter-proof? Sure, the hospital security would be improved, but there are a great many ways to go about fixing the problem without compromising the privacy if hundreds of thousands of people.
People have been trying for years to get the point across that we need to have better security. None of them have managed it. If anything, security is getting worse because cracking tools are becoming more sophisticated. Someone had to get word out, what people were doing to raise publicity wasn't working, there was a way to get attention, and LulzSec did it. Bad as what they did is, they successfully raised media awareness of the fact that those patient records were in a clearly-labeled manila folder taped to the front door.
I'm glad they didn't -- this way I can still have some privacy.
cracking tools are becoming more sophisticated
IMHO, it's easier to break into someone's home than into someone's server.
The result more predictable too, as you can find tools that can crack open doors, windows, anything. And if all else fails, you can just watch the house until somebody makes an error, like leaving the window open by themselves (although experts don't have to do this).
Real security can only be achieved through serious investments into state of the art alarms, safe-deposit boxes and by being a paranoid.
Another way to do it would be to plant GPS devices in each and every human and track each movement into a centralized database, while good thieves will find ways to block that signal anyway; and that's how all of the proposals for a more "secure" Internet sounds to me - basically punishing honest citizens in the name of security.
[Edit: by "good plan" I mean that their plan had a good chance of success, not that it was beneficial. That part is still up for debate.]