We're at war and it's a glaring vulnerability to homeland security, not to mention all the other associated issues. Why shouldn't ALL Americans be concerned?
This is not the major problem it is made out to be and is more of a nuisance than a danger. It is generally just a means of attacking Bush by appealing to the unaware and pseudo-conservatives. Most of those obsessed with this issue never even voted for Bush or if they did bitched and whined about it all the while.
Though a problem from several perspectives II is not the ONLY problem in the world nor is it even the problem those obessed with it try and make it. Most Americans are not even willing to force their local and state authorities to cooperate with federal authorities in enforcing immigration laws and even declare their cities to be "Sanctuary" cities. And the churches are often even worse in their misguided "humanitarianism."
As far as a National Security concern it does not even rise above that posed by the Northern border from whence the only thwarted attack we are aware of came. Canada is the home of far more moslems than Mexico and the numbers are growing.