Religion is an irrational, narcissistic delusion. It poisons the mind and unleashes the id--the quasi-psychopathic two-year old that lurks in all of us. It poisons the mind's ability to think properly by filling it with false "facts" and false standards of reasoning. It makes it impossible for believers even to agree among themselves because they have rejected reason.
They are left with the only tool for settling disagreements when reason has been rejected: Force. And, indeed, their words, their actions, and their history show that they do believe that might makes right. Their holy writings show that their god seems to think the same way, which, to my mind, is yet more proof that he is man-made and made by some very bad men at that. Power should never be allowed to become the tool of a group of people who tend to indulge in a narcissistic rage when their delusion has been challenged. Such people are literally capable of anything.
Even when not in a rage, they will take actions that make sense only to those who share their delusions--in other words, actions that don't make sense. Such actions will have a negative impact on the world around them, including other people. A good example is the unwillingness of many believers to embrace conservation because they believe Jesus is coming back to earth any day now and that the end of the world is near. (They have been believing this for 2,000 years and it hasn't come true yet. One would think by now that they should have figured out what that means.)
This philosophy has the potential to condemn humanity to extinction. My willingness to tolerate the beliefs of others ends when they become a threat to me and my family.
In the past, when the human population was small and technology primitive, cults could find an isolated location so that they did not effect others with the harm caused by their illogical beliefs. (Although in practice they almost never did that, instead they set out to conquer the world, which they continue to work toward to this very day.) Our modern society makes such harmless isolation very difficult--even if some cults try to follow that path rather than the path to world domination that so many are on.