You schleps will justify any effort to undermine the security of this country. Its no siurprise the same people that hate the projection of US military power, hate the rule of law, and hate the traditional American identity also hate the idea of secure borders.
Central American and Mexican gangs have been facilitating illegal traffic at the border for years. Its only common sense that if ISIL desired to smuggle weapons and explosives across the border, they could. As Boaz said upthread, its a vulnerability that IS being exploited by groups hostile to our safety concerns.
There is no bogeyman, theyre DOING IT.