people really need to be with like-minded people.

I think its way simpler than that

Yes, with the emphasis on "multi-purpose". I don't, however, think religion was just an idea that people came up with to solve a problem. I think it has biological roots, along the lines Wathey described, and evo-psych roots. It appears to me to have evolved along with humans since before humans were human, and, along with culture at large, serves as a counterbalance to environmental changes that cannot be met quickly enough by biological evolution.

If religion was only made of ideas we would have easily shed those ideas when better ideas came along. The evidence against that is the many scientists and otherwise well-educated people who are still deeply religious. It's as deeply embedded in our DNA as the impulse to hunger or fear of death. It will not be run out of town by something as flimsy as a better idea. Individuals vary of course, but our species is a religious species, and will continue to be so until we get a lot better at manipulating genetics, or until we evolve out of it or go extinct. In the meanwhile, our best hope of coping with its negative effects is in cultural evolution. That is to say, to create a new cultural counterbalance to offset the old cultural counterbalance. Reform, not abolition. We cannot legislate "fear-of-death" out of existence, either politically or socially. We must find smarter ways to live with it.