Religions were firstly created to aid human civilization with hope, dreams and something to look up to. We are all entitled to our own beliefs and whoever begs to differ should go die in a hole. For some religion like I've said is hope, bereft of religion they may be lost. Then there are others who completely disregard it as pathetic and childish because that's them, and it'd be wrong shoving it down their throats. It's a two-way road, and everything in this world isn't just black and white, there are shades of grey all 'round only too faint so most people don't understand or won't bother understanding.
It's not going to be all that visible from an non-believer's point of view, but most religions do have a better truth claim than some shit someone just makes up off the top of his head. At the very least, their ideas have been "bounced off" a whole bunch of other people, and been refined via adversarial processes and are often very stringent. Any possible critique of any possible religion has already been voiced, and the religious have had to answer for that. Occasionally they come up with answers that even hold water.
My experience with people who follow a sui generis set of beliefs is that they insulate themselves from any critique whatsoever, choosing to answer for nothing at all apart from their right to hold any beliefs they want.
The main difference is that a religion is working with a set of basic fact-like statements constituting (at least in Abrahamic religions) a putative divine revelation that must be taken as it is. A fundamentalist Christian may exhibit an irrational reliance on the Bible over the evidence of the real world, but he is (usually) not free to concoct what the text actually says. Specific teachings are drawn out as a developmental process over a very long time and are almost always founded on the revelation. That may not always be obvious at first glance for any particular teaching, but an educated religious adherent can usually tell you how it was arrived at.
On the other hand, a personal religion might be based on anything at all, even on something as flimsy as an individual's private fantasies. It need not be, and often isn't, self-consistent, and the individual has almost never thought through all the consequences.
I've always been of the opinion that all religions are the same, more or less, the names and stories are just changed, with some more local doctrine by the local culture. Same "God(s)" just different manifestations based on cultural concepts.
But the problem lies where each religion, in order to gain and keep followers (and therefore power), maintains that it is the ONLY "correct" religion (with some consequence to nonbelievers), and that is where the fighting begins...
Just think about ethoncentricism. Everyone has a bit of that. If you talk about American pride, you have ethnocentricism. Everyone has a little ethnocentricism in them. It kind of promotes alot of things, like solidarity and the feeling of you belonging to something. It kind of glorifies history.
But of course, everyone can have cultural relativism. Not all religions are purely ethnocentric. A few people in the group can have respect to others.