If we could get every human fanatically following a single religion, just imagine the benefits! No longer would we have to make an effort to take another faith's interests into account, no more would there be any form of religious friction. A single, monolithic faith would unite humanity under a single symbol. The cross, the crescent, it doesn't matter. All that matters is that humanity would become an enormous mass of energy that could be focused on whatever's best for the species, and accomplish whatever it set it's mind to. I'm not religious myself, but if all of humanity were to worship the same god? I'd keep quiet, and watch what great wonders the species could cook up next.
(NOTE: I think Islam would be a good choice, or something collectivist. Buddhism and Hinduism seem to be too passive, and Christianity seems to be a bit watered down these days. And forget the weird little cults. We've got plenty of mosques already, so we oughta use 'em.)
I don't think religion is the problem because at the end of the day and at the end of our lives its all one god, whether we are Christian, Muslim, Jewish, Buddhist etc. World peace, yes, but the hatred amongst one another isn't religion, its what humanity has become, basically, what we did was turn religion into a worse version of politics. War nowadays is mainly because of some religious confusion, take the terrorism of the IS for example. Everyone is bashing on Muslims for the misunderstanding and misinterpretation of the Quran, the IS have everyone thinking Islam promotes war when I've read what it says and its the most forgiving thing I ever read. This is just another example of how it isn't the division of religion corrupting world peace. I think if we put religion on the side instead of putting it into everything and every little argument we'd be much closer to world peace.
Everyone will have peace. The more religions there are, the higher the chance would be for people to go to war. I think that it is ridiculous how people fight over beliefs. I don't understand how people could just live on n harmony by living with only one religion that everyone can follow.
It is human nature to disagree and if everyone were forced to join 1 religion; terrorism and rebellions would quickly ensue. We are much better off making our own decisions and living our own lives, choosing our own deities or choosing to have none. That is the best way, I think.
Listen, I'm no Christian, or Catholic. I'm Wiccan. Many people are not okay with that, but what do I care? It's my life, and the religion I want is the religion I'm going to believe. (I humbly apologize to Christians, and people who worship God and Jesus very strongly), but I don't want to believe in those things. I don't want to go to church. I will always believe in God, always, but I want to be a Wiccan that makes potions, and doesn't think about Jesus. (As I said, that doesn't mean I don't believe in them.)
I tend to believe God speaks to different people in different ways. In that respect, the entity or all-knowing spirit we refer to as "God" can be Jesus, Yahweh, Allah, Vishnu, Buddha and more, depending upon one's believe system. Everyone should not follow the same religion unless there is some massive revelation by God that everyone sees equally regardless of one's belief system.
If everyone where to follow the same religion, which seems improbable without some form of brainwashing, humans will have had to lose part of their identity. Also, just because everyone is following the same religion, does not mean that it is yours. If everyone had to become Wiccan, there would be an uproar, but if a more popular religion (perhaps what you believe in?) where picked, it wouldn't be a big deal.