It would only make sense for the NSA to monitor sites that encourage violent behavior against the United States of America. I do not think there is anything wrong with doing that. While I think that such sites are wrong, I do not thint that they should be banned or anything like that.
I don't believe the NSA should be in the business of tracking all the websites globally that are anti american, there are likely to many of them and most of them are likely not serious enough to dedicate any resources on in the first place, the NSA should concentrate on clear and concise threats to America.
This is a silly idea to me, and just adds to all the paranoia there already is in the United States and around the world. I have been traveling for years, and I see increased levels of paranoia and anxiety, even though the world has gotten steadily more peaceful over the centuries.
Speech is free and protected in America, and it is not our right to covertly monitor or spy on people of any country writing invective against the country. These are, after all, only words and not actions. If there are truly terrorists operating in the digital sphere, I believe they are smart enough to not to post anything critical or revealing about their plans and actions on public webspace.
Sedition is conduct or speech inciting people to rebel against the authority of a state or monarch. I do not believe the NSA should monitor the Internet for websites that allow sedition against America. Citizens should have the full right to freedom of speech included inciting people to rebel against the authority. Inciting doesn't indicate action and it also doesn't indicate that the incited incidents are inherently illegal.