Islam is a theocracy.
Islam, therefore, is more than a religion, more than a culture, more than a way of life, it is a governing system.
Islam explicitly rejects toleration of competing religious, political, and cultural views.
Islam explicitly rejects the legitimacy of other religious, political, and cultural systems.
Islam explicitly aims to incorporate every mortal on earth into its political, cultural and religious system.
Islam explicitly endorses "jihad" as a legitimate method of extending its system.
Jihad explicitly embraces violence as a method of propagating the Muslim system.
There are 1.6 billion Muslims on earth.
A substantial minority of Muslims explicitly endorse terrorism as a legitimate tool of jihad.
Terrorism employs violence, including murder, to achieve political aims.
Terrorism's tactic is to incrementally intensify murderous violence to instill fear, to demoralize and to ultimately cause the polity to surrender.
Terrorism's strategy is to force representative democracies to either resort to repressive countermeasures or surrender.
Ultimately, a representative democracy which accepts a critical mass of Muslims into its midst will be forced to choose between surrender or tyranny.
Ultimately, a non-Muslim system which accepts Muslim immigrants will be so beleaguered by terrorism that it will be forced to choose between surrender and gulags.
It is more democratic and less tyrannical for a democracy to halt Muslim immigration than it is to defend against Muslim terrorism by increasingly repressive methods.