Although I do not think that governments should have official national religions under any circumstances, I can understand arguments in both directions. Let us examine these arguments.
We could argue that it is good to have a national religion for at least two reasons. First, if people truly believe in the religion, it might help with social control. People might be more obedient and more law-abiding if they believed in the national religion. Second, a national religion could be an important way of promoting solidarity in a country. It is important for the people of a country to feel that they have something in common. If all the people of a country believed in the same religion, it would give them a bond. That would help make the country more socially stable.
However, I believe that the arguments against this outweigh the arguments for. If people are forced to profess a certain religion, they may well rebel. They may not actually take up arms, but they might be angry at the pressure to believe certain things. This would defeat the purpose of the national religion as expressed in the previous paragraph. In addition, freedom of conscience is an important right. If governments can tell us what religion to adhere to, what other things might they order us to do?