Recently the United Arab Emirates imprisoned six Islamic supramacists because they had refused to seek alternative citizenship after the UAE had revoked their status as citizens. The six Muslims were asked to leave their former country because they are considered a threat to national security.
People should not be citizens of the country they wage war against. Nor should those who preach or teach terror. After having served their sentence, they should not enjoy membership in the society they tried to destroy, but should be expelled without the possibility to return.
Depending on the definition of terrorism, such laws could be very relevant, should Muslim-dominated areas inside our countries create physical fronts and show violent and persistent hostility towards the state. Whoever does not voluntarily leave such violent self-declared autonomous areas when asked to do so by the authorities could be considered a terrorist with the aim of using violence and threats in order to remove the rule of law in parts of the country, provoke a state of terror in the general public to obtain religious or political goals, or even achieve some degree of secession.
Considering the speed of how violent hostility towards non-Islamic authorities and non-Muslims in general grows in thousands of Europe's Islamic ghettos, we are witnessing what could be a prelude to the no-longer-so-unthinkable: the illegal borders, guerrilla warfare, terror and kidnappings that have always characterized the borders between the Houses of Submission and Jihad -- Sharia Land and the infidels.
Confronted with an organised attack -- whether staged by lone wolves, groups or whole city blocks -- with the aim of destabilizing or destroying our countries, citizenship should no longer be unconditional.
Endnote: related articles of mine "Integration, immigration and Islam-related problems: 23 suggestions for laws" and "What is Islamization? An incomplete list."