I believe that governments should be secular because not all of the people living in the country will adhere to the same religion. It would be alienating for those who didn't practice and I feel that endorsing a particular religion would just reinforce animosity, negative feelings and prejudiced acts towards those who didn't follow it.
It is the government's job to be religiously neutral. There is a separation of church and state. The government would be considered the state. It would be unhealthy for the country if an entire government decided to back a certain religion. Although many Christians would like for the government to back their religion, they wouldn't be so enthusiastic if it was Islam that was being backed.
http://www.libertylawsite.org/liberty-forum/the-illusion-of-religious-neutrality/ heres the beginning
“The Establishment Clause cannot be reduced to a single principle,” Christopher Lund observes in a recent article. “But if it could–if there is a single premise that has animated the Supreme Court’s approach over the past fifty years–it would be the neutrality principle. Government must be neutral toward religion . . . .”
Indeed, for reasons we will notice, the proposition that government should remain “neutral” in matters of religion appears to be virtually irresistible. Which leads to embarrassment: that is because, upon closer inspection, religious neutrality also turns out to be impossible. Worse yet, the attempt to maintain religious neutrality subtly works to undermine the constitutional commitment to religious freedom. This essay briefly considers the predicament and reflects on possible responses.