I actually don't think Ned was dumb. I just think he was too honorable and kind. If he had've gone to Robert as soon as he knew about her children and had her arrested immediately, he would've lived. So would his family. Maybe. The Lannisters probably still would've started a war. However, I think the power would've been on his and Robert's side. I think the thing that pisses me off most about Ned is that his need for honor and mercy ended killing his family and endangering his children.

Catelyn...she did some stupid stuff. But I don't look badly about her as everyone else does. She was a mom looking out for her kids. Then her husband was murdered and her children held hostage (well, they all assumed Arya was in King's Landing). Her oldest child started a war and she was worried there. So yeah, while she did stupid stuff, she wasn't thinking clearly and she did it out of love. I think that's forgivable.

Robb just literally couldn't keep it in his pants. He didn't marry Talisa (or Jeyne in the books) because he got her pregnant. She got pregnant after (and in the book I don't believe it's confirmed if Jeyne is, isn't, or ever was pregnant). He married her because he had sex with her and he had to be "honorable" and marry her after. And because of that, he became an oathbreaker. He had a very good chance of winning the war if he had just been able to control himself for a few minutes. Everyone told him not to cross Walder Frey or make a deal with him lightly, but he didn't listen.