And despite this deathless rhetoric in the face of economic collapse, FDR interned 110,000 Japanese people because they had distinctive ethnic features shared by one group of people engaged in a war against the US, although there was never any attempt to intern German-Americans.

What happened in the Boston is that the authorities requested the cooperation of the public in exceptional circumstances, and got it. If they had tried to impose some sort of lockdown on Monday after the bombing, you might have a point. But they didn't. The city kept operating normally until the suspects resurfaced, got into a shootout with police, and one of them managed to evade his pursuers. Given how many people were affected by the original terrorist incident, I don't find it odd at all that most people chose to facilitate the manhunt by leaving the streets empty.