I agree that oily fish, such as sardines, are an excellent source of omega-3 fatty acids, among other important nutrients. But there are just too many humans and not enough verifiably sustainable fisheries out there, trawling and seining the seas, for this to be a regular part of everyone's diet. (And fish-oil capsules are even worse: you cannot regulate what goes into them.)
What Ms. Beck and every other dietician who has written about this neglects to mention is where fish get their fatty acids. They don't synthesize it themselves, they get it from the seaweed/algae they eat, either directly, as herbivores, or by eating herbivorous fish. We should skip the middleman!
With the proper programs, we *could* feed 7 billion+ people with seaweeds. They are easily cultivated, compared to fish, and far less destructive to the environment.