The problem many conservatives have with the current immigration program is that new entrants don't plan to assimilate, and in many cases they're encouraged not to.
Now we learn that Obama Seeks Admission for 10,000 More Syrian Refugees. From what we've seen of Obama, it probably won't stop there.
It would be nice to think they'll assimilate and become good Americans. But that's probably a wild dream as that hasn't worked out all that well lately. See Ian Tuttle's Before Welcoming Thousands of Syrian Refugees, We Should Consider What Somali Immigrants Have Brought the U.S. Never mind the burden those individuals have put on government assistance programs, they tax the shelters, food banks, and local charities as well. And there's this:
But, as the Somali experiment makes clear, it is not just the short-term consequences that are worrisome. Notably, the terror threat from the Somali-American community comes not from refugees, but from their children — American-born Somalis who have never been to Africa. Setting aside the near-certainty that at least some Syrian refugees will be connected to the Islamic State, refugee resettlement is sure to incubate national-security threats that will not manifest themselves for 20 years. ...
We know much more now about the threats we face, and we have the Somali community as an example of the consequences of a generous refugee policy in an age that eschews assimilation. It would be entirely humane to rescue those suffering from Syria’s mayhem. It would be inhumane, though, to gravely threaten American security in the process.
It has already started. See The Twin Cities have an ISIS problem.
Images like the dead kid on the beach tug at the heartstrings. It takes courage to resist being led on a leash by a need to be liked.