The difference being they aren't standing around on everyday street corners with fully loaded automatic weapons.
Correct me if I'm wrong, but the caption on that particular image stated that it was taken in 2003, when there was a specific instance of a credible threat against New York City. (The caption gets the alert levels wrong, as well.) I'm not a New Yorker myself, but I'd doubt that you'd see guards stationed there on a daily basis under normal circumstances. What's more, those were National Guard units, who have been serving in roles such as augmenting airport security for some time now.
From a different article:
They may be called upon to help with civil unrest and crowd control or to deal with potentially horrific scenarios such as massive poisoning and chaos in response to a chemical, biological, radiological, nuclear or high-yield explosive, or CBRNE, attack.
The second part is understandable, but the first part sounds more like policing.
Correct me if I'm wrong again, but that quote sounds to me as if both parts are referring to the eventuality of some sort of attack or catastrophe, or at the very least, that the first part would be tangentially related to an event along those lines. I see nothing to suggest that active soldiers would be taking the place of SWAT units at a local protest.
A.) That was the National Guard and B.) that was a special request. You don't see any of those guys in New Orleans anymore, do you?
Actually, as the very
article you linked mentioned, several active-duty units were called in after Katrina.
Really, I think we all have enough issues regarding civil liberties to worry about without having to invent additional hypotheticals.