By closing borders you can be sure that ONLY the violent ones cross your borders.
Because peaceful ones will be less likely to risk their lifes than the crazy terrorist ones :/
And you think you can close your borders efficiently... Then think again xD
Yes. The borders can be closed effectively. Look at Israel, which is neighboring Syria. Why hasn't any of the immigrants from Syria gone to Israel? Israel has shown to the world how to defend itself against the immigrant invasion.
Right. Of course borders can be closed. Just try to sneak into Saudi Arabia.