Originally Posted by JediMastr
HE TOLD THE QUEEN HE KNEW AND SHE ADMITTED IT!!!....sigh, and then asked her politely to leave before he told Robert?
What were Ned's options: (1) Do nothing. (2) Spill the beans to Robert, which would result in the three children being killed (and quite likely war). (3) Tell Cersie and hope that she took the children and ran in disgrace.
The problem with option 1 is that he'd have to swear fealty to someone he knew was the wrongful king, and his honor wouldn't allow it. Option 2 would be a mess...no matter how much you might hate Joffery, there's two little siblings also, and they don't deserve to die just because their father isn't who they thought it was. Plus the whole war thing. Option 3 really isn't "stupid", just overly optimistic that Cersie will abandon her pride and ambition for the sake of her children's safety and peace in the realm. Considering Ned's character, it is the best of three bad options.
Ned knew she might not run, which is why he moved quickly to set up a backup plan. He should've taken Renly's swords, but if Littlefinger hadn't double-crossed him, nobody would be calling him stupid.