Plenty of people have died for their beliefs; comparatively few have been put to death for claiming not to know anything. Socrates was a martyr to the Socratic method, which amounted to a kind of studied ignorance. Of course, the formal charges against him had nothing to do with his method of inquiry. He was accused of being a corrupter of the young, an atheist and a believer in supernatural beings of his own invention. Socrates, true to form, could not resist pointing out that the charges weren't even internally consistent, since you can't be both an atheist and a believer in supernatural beings, invented or otherwise. It was precisely this penchant for showing up his opponents that eventually got him killed.
The chain of events leading up to Socrates' trial began, appropriately enough, with a question. His old friend Chaerephon asked the Oracle of Delphi whether any man was wiser than Socrates and was told there was none. Socrates, of course, would never make such a claim for himself, nor was he prepared to accept it from another, even on the highest authority. He therefore set about to prove the oracle wrong but succeeded only in demonstrating that everyone else was even more ignorant than himself. In the process, he discovered that those whom he subjected to the Socratic method did not appreciate being made to look like fools.
Socrates expected to be found guilty and was not disappointed in this, although he expressed mild surprise that the vote was actually relatively close. However, any sympathies he may have enjoyed at the outset were quickly squandered during the penalty phase of the trial. Given the opportunity to propose a lesser sentence than death, he suggested he be given free meals at the Prytaneum in return for his services as a gadfly. And far from complaining about the severity of the punishment as originally proposed, Socrates suggested that death was at worst a dreamless sleep and at best an opportunity to hobnob with the likes of Orpheus and Homer in the nether world. Not surprisingly, the vote in favor of a death sentence was far more lopsided than the initial verdict against him.
In many respects, the Socratic method is an exercise in what Zen Buddhists call "beginner's mind." It is a frame of mind that assumes nothing and accepts nothing on authority. It is animated by a pure spirit of inquiry that begins with no end in view. Its purpose is not to acquire knowledge, since knowledge can only tell you where you have gone before. Socrates was determined to remain unfettered by the accumulation of knowledge and experience that usually passes for wisdom. For Socrates, there is no wisdom apart from God, and that is the wisdom of not knowing.
Plato, The Apology