Why Some Governments Prohibit Non-Muslim Missionary Activities?

Some Islamic countries forbid missionary activities of other faiths or ideologies because of two major reasons:
1. The whole citizenship or the majority are Muslims and they have chosen Islam as their way of life, to secure felicity in this life and in the Life Hereafter. This means:
a) To believe in a creator for the whole universe, Allah, glorified be He.
b) Allah alone deserves to be worshipped.
c) All creatures can communicate with Him directly.
d) Allah distinguished the jinn and human beings with abilities, such as reasoning faculty and relative freedom, and provided them with guidance in the form of the natural disposition of man and the Divine messages through God’s messengers. Therefore, they have to account for their deeds in this temporary life and to reap their fruits in the Eternal Life, where there is only Paradise or Hell-Fire.
e) It is necessary for the accountable beings (the jinn and humans) to obey the commands of Allah; i.e., to do what they are commanded to do and to refrain from what they have been forbidden.
Thus, it becomes clear that current religions and ideologies contradict the Islamic religion in one or more principles. Promotion of these religions or ideologies threatens the security of the Muslim citizens, not only in this life but also in the Eternal Life.
2. A great percentage of the citizens are not adults, and the government is responsible for their safety including their fate in the Eternal Life. But those who live outside their countries, whether they represent themselves or represent their governments, the governments do not prevent them from exposing themselves to the alien faiths or ideologies. In fact, the adults who are qualified to expose themselves to these religions and ideologies are often helped to study them.
This law is actually in harmony with the international codes concerning cultural rights, which grants the parents or the guardians the right to choose the type of education for their children.([1])
It is natural that some governments prevent some activities because from its own point of view they are dangerous activities that undermine the internal security of the country, even when these activities endanger only the temporary life of the citizens. This kind of law, which is approved by the ‘democratic’ systems, becomes more critical if these activities endanger not only the temporary life but also the Eternal Life of the citizens.
In fact, as long as these laws do not pose any imminent threat to others, they are in harmony with the Charter of the UN, which emphasizes the independence of its members, and protects it.
Aside from the law that prohibits missionary activities, all Muslim countries, one way or another, permit non-Muslims to practice their faiths and to apply their civil laws, provided that these laws are not in conflict with the laws chosen by the majority in the country. This common practice by the Islamic countries is derived from Islamic law, which also gives a special status for the area occupied by the Kingdom of Saudi Arabia, the host of the two holiest cities to all Muslims in the world.

([1] ) the Human Right Resolution, article 26: 3; International Agreement referring to
the Economic, Social and cultural rights 13: 3.