I guess we'll have to agree to disagree here. Ask yourself what would have happened if NEd hadn't agreed with Varys to disavow his previous words against Joffrey? Do you honestly think they would have let him go to the town square and shout his accusations to the public. HELL NO!! He woulda died in that cell with Rats and shit all around him.
I'm gonna paraphrase the writer Martin and what he's said about the way Ned went out. He basically said that people need to understand is that characters SERVE the story and not the other way around.
It served the story for Ned to die the way he did, because if he does not then we don't get to see Joffery go back on his promise which more than anything added fuel to the fire of his enemies. Joffrey was going to have problems anyway, but now he's added additional justification for his enemies to work with.
On the other hand if he had been the stiff honor bound character you seem to want him to be, that's exactly how he would have died in that cell serving no purpose but his own.
ask you to reflect on Ned whole character. Yes, he's shown to be almost always protecting his honor, but he's also shown to have emotion and care for others. See how he acted to prevent Dany's assassination, not just because it was the honorable thing, but because he knows he has to protect his own family member from the same kind of retribution. Allowing Cersie a chance to leave was not truly the honorable thing to do but again he has to consider his own illegitimate family members.