To better understand why conversion to a religion promoted or dictated by a sultan is not rational, some historical examples and precedents should be considered.
Historically people who were converted to a new religion upon its imposition by a sultan generally brought many rituals from their former religion to the new one. Over time, this leads to strong interaction between the two. However, the basic goal of a religion is to make a distinction between true religion and false, which makes this a problematic relationship.
Subscription to a religion is an individual decision. From this perspective, choosing a religion requires purging the remnants of any former religion from the soul and the heart. Once you are sure that the prophet you are following is a true prophet, you do not consider his miracles; instead, you consider whether the prophet's message is confirmed by our conscience and reason, and whether its precepts best serve the interests of society and humanity in general. If our conscience endorses this message, and if our hearts are enlightened by that message, we conclude that it is coming from an authentic and sacred source carried by a great messenger.
The subject of a sultan -- or a citizen under the influence of the state in modern times -- does not have an individual conscience, heart or mind that acts to fulfill his goals. The determinative factor in the attitudes of people who convert to another religion because it has been imposed by a ruler is the collective mind reinforced by the blood bond (ontological impulse and reflexes), rather than internal considerations created by the religious message in the individual's heart. The collective mind created by the blood bond is usually a ghetto for the individual mind, a prison whose walls are made up of habit and strong tradition.
As noted by Ibn Khaldun, in this case, bonds of ethnic origin are above everything. However, religion, as a call of emancipation, asks its followers to move toward some sort of union of objectives. It also ensures that by virtue of the new mindset created by the merger of free minds, they function within their religious community as separate individuals belonging to a strong united group. However, the individual's free choice does not mean that the individual is isolated from others. Religion also asks followers to live in a community. The individual within this community is not like a grain of sand: He or she is part of a larger group created for the fulfillment of a greater objective. He or she is an independent person like a single tree, but he or she is also part of the forest. Allah's hand is upon only such communities. The separate individuals as well as the communities they create, considered as blessings from Allah, may convert the earth into paradise over time.
Big states or empires have never been able to convincingly impose their religious choices on their peoples. They were generally unable to convert all of the people to the religion of the state's choice, and even those that did do this were unable to sustain it. However, even if it seems strange at first glance, the subordination of the people to the state through centralized forced decisions, as well as social projects designed to build nations and the state's insistence that its subjects subscribe to a religion chosen by the state, became popular in modern times and in modern nation-states. For the first time in history, the modern state attempted to build new nations and new societies through a totalitarian and integrated mission; therefore, in an attempt to legitimize the state's ideology, it pursued totalitarian policies to ensure that the people quit the religion of the sultan.