Yes, most people fear the unknown and it might be a comfort to believe in God and an afterlife to reduce some of that fear. Granted, religious leaders have sometimes used the church and people’s beliefs in un-Christian ways. But that doesn’t necessarily mean that God doesn’t exist.
You seem to imply that the only security that Christians get from their beliefs is that everyone else (or a large number of people) believe the same. You keep referring to a fear of the unknown. The only unknown I can think of off the top of my head is what happens to us after death. Will I be judged? If I am judged, will I be judged favorably or unfavorably? If that were the only purpose of organized religion then I think that they would have come up with some easier requirements, they would get a lot more followers. In general (and I’m sure someone could nitpick this to death) Christian beliefs deal mostly with leading a ‘good’ life. Don’t kill, lie, cheat, or steal. Treat others with respect. Help those less fortunate than yourself. Actively work to make the world a better place. To me that sounds reasonable but sometimes incredibly hard to do in real life.
Your view is quite pessimistic. To think that the reason religious leaders condemn suicide is that it would undermine their position is extremely cynical. A human life has incredible potential. And I’m talking ordinary people here. Hasn’t a smile or a kind word from someone brightened your day? Maybe it caused you do something kind for someone else later on? We are given this life and we leave a legacy as a result of how we touch other lives.
I’ve lost three cousins to suicide. If ‘making it a sin’ could have kept them alive then I’m all for it. Their grief and pain were transitory. Their situation would have gotten better. Suicide is the ultimate ‘I quit!’, and when you quit it will never get better.
I hope you don’t take any of this as a flame or assume that this is meant to be derogatory in any way. There are some religious leaders that abuse their power, some that preach one thing and do another. There are some members of organized religion that seem strident and/or obnoxious. That may influence your attitude but it doesn’t necessarily invalidate their belief system.