“After something like that happens, they should stop all visas, for crying out loud,” said Ms. Kontis, 58, who owns New Wayne Pizza with her husband, Alex. “It’s insane. It just angers me.”

Ms. Kontis was born in Greece and immigrated to the United States as a child, but when two men of Chechen heritage were identified as the suspects in the fatal Boston Marathon bombings, her usually broad views about immigration became colored by concerns for national security.

“That is who’s coming in,” she said. “We don’t know what kind of people they are. The bottom line is we have to stop being goody-goody Americans.”…

But that message was not always embraced. “I’m a little more of an extremist now after what happened in Boston,” said Greg Ricker, 41, a stockbroker, as he stepped outside the Flying Pig Saloon in Malvern for a cigarette. “I think we should just stop letting people in.”